Many people asked me if a melee Zero is viable at the earliest game stages, claiming that it's better to start with headshot, or the cunning tree. I made this guide to prove they are wrong: a melee Zero is viable even from level 1, when there are no skillpoints available.
This is the way I find more efficient to level up my Zeros. There are different playstyles, and different tastes on weapons and skill choices, and especially in normal mode everything is viable so in this guide I'll just show the way I find easier to play a melee Zero and explain my choices and preferences and the reasons behind them.
Sorry in advance for all the grammar mistakes you'll find in this guide but English isn't my native language.
I'm using a new character as template to write this guide. I'm trying to not be overleveled during the game to maintain balance. However, if you do all the sidequests things will change a lot (like gear or quest rewards availability per level) so don't take my advices too seriously since they are based on an average, non overleveled character. I'm not mentioning DLCs too much to keep the things very simple and linear.


From Lvl 1 to Lvl 4:
No skillpoints are assigned for the first few levels, but both weapons and melee are very effective so it is possible to have fun with whatever weapon or playstyle we prefer. A single critical melee hit can kill the weakest enemies like monglets, psychos and marauders, especially if they are below lvl 4. However it is pointless and dangerous to get too close to enemies this early in the game unless you want to have fun with melee.

Recommended gear:
Basic white weapons are very effective at early levels. You will find mainly pistols, rarely shotguns, assault rifles. Shields are usually basic tediore shields, just pick the best you can find along the way. A fundamental weapon you really can't miss is Hammerlock sniper rifle from the quest "bad hair day". I recommend to take this quest as soon as it's available. Remember to always turn the quest in to Hammerlock! This will be the only sniper rifle you'll ever find for a long, long time and it is a life saver in many circumstances. It can oneshot almost everything all the way up to Flynt as long as you can crit.

Level 5:
Deception. At level 5 you will be able to activate your action skill. A well placed melee hit boosted by deception can oneshot shielded enemies, and deception always helps to run for cover if the enemies are overwhelming.

From Lvl 6 to Lvl 10:
Killing Blow (KB). Killing blow is an incredible finisher. Everything that can't be killed in one shot, will die in one shot and one stab. Simple as that.

Why not Iron Hand?
Iron hand melee damage boost is very small, and the extra health is not needed this early in the game. Actually more health might cause troubles with healing especially in early game where healing sources are scarce.

I've heard...
Some people say 5/5 in KB is overkill for mobbing and suggest to only assign 1 point to this skill and the rest to Iron Hand. This is false: badass enemies and minibosses needs several 5/5 KB hits to actually die if your roid damage is not active.

Recommended gear:
From level 7, more weapon types will spawn. SMGs, sniper rifles, RPGs, the first AoE grenades and later Class Mods. A gamechanger weapon will be the Lascaux, remember to grab it before the firehawk fight. A bladed version is ideal.
Eridium?

• The most important ammo for a melee zero are grenades so be sure to grab extra slots for them. Vladof AoE grenades are immensely powerful in early game, and teslas are great against everything, from armor to flesh.
  
• Sniper ammo are also much needed.
  
• Extra backpack space is good for picking up garbage and sell it to the vending machines for a few extra cash just in case something tasty spawns in the shops.
  
• Smg ammo might also be a good idea especially if you are using a Lascaux as main weapon.

From Lvl 11 to Lvl 15:
Be Like Water. I personally find Be Like Water the most rewarding skill to take for early levels. In fact, without many must fall, the player tends to shoot enemies to bring them in KB range and then kill them with one melee hit. It will come natural to shoot-and-stab, shoot-and-stab, so the player will get the most from Be Like Water.

Why not Iron Hand?
Again, Iron Hand melee bonus is small and the extra health is not necessary or even useful. Be Like Water will give a bonus to both melee and gun damage, and will be triggered very often because of how early melee playstyle works. Iron Hand will be useful after getting a Rubi, and later it will help keeping Many Must Fall chains up.
So when should I take Iron Hand?
Sooner or later, the stab-and-shoot playstyle will be replaced by a stab-everything-no-matter-what playstyle. When you realize you are not shooting that much anymore, Be Like Water will became obsolete and you might want to swap it with Iron Hand.
There is no rule, and the change happens gradually, but usually the melee playstyle become prevalent after getting a Law, a Rubi, Execute and maybe Backstab.

Why not Grim?
Actually Grim is good even for a melee build this early in the game. However it kills your roid shield and you definitely need to get rid of it as soon as you reach Many Must Fall, so we better not develop a bad crutch, right? Zero strenght is also his high DPS, so I find more appropriate to prioritize offensive skills over defense: he is a glass cannon and his survuvability is tied to his ability to deal damage.

Recommended gear
Be Like Water extra damage is only applied to the first shot. To get the best out of it, high damage per shot weapons should be used. Shotguns, revolvers and snipers are the best choice.
If you can find any bladed version of them it's even better.
The best relic for Zero is a Proficiency relic ( Increases Action Skill Cooldown Rate) because more deception means more damage and more survivability.
The ideal class mods at this stage are Infiltrator, ninja or even spy. The Teapot from Tiny Tina's quest "Tea Party" can be very helpful against bots and the next story boss.

level 16
EXECUTE: This is the first, true gamechanger. This skill is what allows melee Zero to kill almost everything in one hit, and to close the range very quickly even from long distance.
Why not...
Dude... Really?

Recommended gear
Thanks to execute, Zero will start to hit really really hard. The classic attack pattern (deception -> shield stripping tesla -> roid boosted execute) will be more and more viable, and now even badasses can be one-shotted. At this point, a roid shield, a bladed gun, and a tesla are recommended.

• The roid shield should have the highest roid damage available, a recharge delay of at least 3 seconds, and a capacity low enough to be stripped by a single average tesla.
  
• The ideal tesla grenade should have 0.0 to 0.6 fuse, and the delivery should be longbow or lobbed. The grenade damage should be just right to completely strip the roid shield you have equipped.
  
• The ideal relic is a Proficiency relic to improve action skill cooldown. More deception, more invisibility, more survivability, more executes, more kunai and deathmarks at higher levels. Strenght relic are not good because they are additive and the damage added to the melee formula is extremely small. Override cooldown does absolutely nothing to Zero. Zero's only melee override skill is Execute, and Execute has NO cooldown, so the melee override relic has simply nothing to improve for this character.
  
• The ideal class mod is a Ninja com with bonus to Backstab and KB (Shadow Ninja). Alternatively, infiltrator and spy are not bad in early levels. At endgame a Legendary Ninja (UVHM2) is a must. A special mention to Legendary Hunter for its versatility and increased survivability thanks to health regeneration and boost to action skill cooldown.

Where do I find the equipment? Literally everywhere, from every loot source.
Alternatively all the needed equipment can be easily obtained by farming vending machines. Usually an higher level white or green tesla will strip a lower level roid shield, so you might want to farm the ammo shops that provide you the higher level equipment: to find them, travel to the area whith the higher level enemies and check the vending machines. The items for sale are usually the same level of enemies.
At this level it is possible to obtain a Rapier from Scarlett DLC. A 200% melee damage bonus will make a huge difference! However I'm not going to use DLC gear in my reference playthrough to keep it as much linear as possible and avoid overleveling.

I can't kill that Pyre Thresher... I know. You'll find the first one at level 16, and it's not possible to oneshot it with the equipment available this early in the game. Your only healing weapon is the heartbreaker which is always fire elemental so it's completely useless against pyre threshers.
My suggestion is to throw all your Teslas at it, execute it once and then finishing it from FFYL. Alternatively, leave the quest for later and level up a little bit. Getting a non-fire Hail can be very helpful.

From Lvl 17 to Lvl 21:
Backstab. Backstab is a core skill for all ninjas: the damage bonus is multiplicative and it can get crazy with execute. Obviously enemies must be hit from behind for this skill to proc.

Why not Followthrough?
Followthrough is an amazing skill we'll take right after Backstab. Backstab is a priority because it grants an higher melee damage and it is boosted by ninja class mods. Since the damage is multiplicative, you definitely want to have it at 5/5 or higher as soon as possible.

Recommended gear
At this stage, a few Moxxy weapons can be obtained:

• Hail from the Bandit Slaughter Dome is the first one available and it's really effective after you learn its odd firing pattern.
  
• Heartbreaker (remember to turn the quest "Safe and Sound" to Moxxi) is the second one available and it is an extremely powerful fire shotgun.
  However their healing effect of the aforementioned weapons is very small and it's not something you can cout on if the weapon is not bladed.
  
• Law this is the first real gamechanger: an high damage bladed revolver granting a 100% melee damage bonus. If you don't have a Rapier from DLC1 the Law is the second best option.
  
• Love Thumper: after the Overlook story mission, from lvl 16 up, you can obtain the Love Thumper. However I discuorage anyone from using it this early in the game: the Love Thumper is powerful, easy to manage but without a reliable healing source it leaves you with very little survivability. For this reason I suggest to use the love thumper after the quest "rakkaholics anonymus", when a bladed Rubi will hopefully be in your hands. However don't get too attached to this shield: as soon as you find one with a better roid damage, drop the Thumper.
  
• Bladed Rubi will be the next gamechanger. Healing will be much easier, and it will be possible to tank enemies without worrying too much. I recommend a bladed rubi, the element is not important as long as it has a blade. In normal mode slag is almost irrelevant.
  
• Last advice: if you need high level weapons before the Wildlife Exploitation Preserve story mission, you can take the quest "Slap Happy" from Hammerlock and farm Old Slappy. He has high chances to drop purples and blues and they should always be WEP level.
  Roland loves Ninjas and he will often offer blue roid shields as quest reward.

From Lvl 22 to Lvl 26:
Followthrough. Followthrough is a key skill in almost every Zero build. It grants you more gun damage, more melee damage, and more movement speed after killing an enemy. At higher levels it really synergyze well with Many Must Fall and Innervate. The increased movement speed helps closing distances for chaining MMF and aids with the positioning for backstabs. Followthrough damage bonus are additive in the melee formula, so the bonus is very small: the main purpose of this skill is the movement speed.
However, Followthrough synergize well with Be Like Water.

Why not Resurgence?
The healing from Resurgence is very, very small. It is not enough to improve survivability at this point in the game.
It's also relatively useless since our main healing source is the Rubi.
However Resurgence will make much more sense when reaching Many Must Fall: chaining kills while stealthed means you'll be able to heal even while wielding a Rapier.

What about Iron Hand?
At this point you might want to respec and get rid of Be Like Water to replace it with Iron Hand. This might not be the case for everyone, because it all depends on your playstyle: do you still shoot-and-stab regularily or are you just either shooting or meleeing? If the first case is true, keep BLW. If the second case is true you might want to grab Iron Hand instead.
In any case, after reaching MMF you definitely want to leave BLW and take IH.
Personally, I prefer to keep BLW until lvl 31.

Recommended gear
Lynchwood is the best place to farm for higher level items if you need to gear up before the Bunker. I recommend to get a nice corrosive sniper (better if vladof, Dahl, or a Rakehell) just for emergencies.
The Morningstar is another nice item to have especially if its element is slag or corrosive.
After the Bunker story mission, you can obtain an Order shield. The Order is an essential item and it will be great for the next few levels: the hardest part will be farming for an acceptable Tesla but it is possible to use 2 nades to strip it.
The Law and Order combo is perfect for tanking enemies without worrying too much about taking damage, because the healing after every melee strike is huge.

From Lvl 27 to Lvl 30:
Resurgence. Resurgence is redundant as long as you are using Law and Order, but if you are using a Rapier as damage dealing weapon it might be a little bit helpful. However this 4 skillpoints are not important now and they can be placed everywhere depending on your playstyle and personal tastes. However you definitely want resurgence when you reach lvl 31, when chaining kills allows you to heal without the need of switching to Rubi or Law/order. The ability to heal costantly while keeping MMF going with a Rapier equipped all the time makes really a big difference.

What about Like The Wind? You can take it instead of Resurgence, it's up to you. The benefits from either LTW or Resurgence aren't really important at this stage. Like the wind bonus damage is additive, so the benefits are very small anyway. But after reaching Many Must Fall, especially if your Order is obsolete or if you are using a Rapier, Resurgence is recommended.

Recommended gear
After reaching the Badlands, I suggest you to do the side mission "Uncle Teddy" and turn it to Una. She will give you the Lady Fist which is the gun with the highest critical hit multiplier. Farm for a corrosive variant: it will literally melt everything with a critical spot, like constructors, loaders and even the warrior.
For Hero's pass I recommend Law, Order, and optionally a Rapier and a corrosive Pimpernel if you have DLC1.
The Love Thumper is too old by now. It's important to have 0.0 fuse longbow or lobbed Tesla for fighting the Warrior.
Again, I suggest you to check Lynchwood: the enemies will scale to your level, and there are many chests and minibosses to farm:

• You can get a brand new, updated Law from the Sheriff, a badge, blues and purples. Don't forget to check the chest!
  
• Mad Dog drops the Baby Maker [Madhous if patched] and has a nice chest in his area.
  
• Dukino's Mom drops the Mongol, together with blues and purples.

lvl 31:
MANY MUST FALL (MMF). The capstone of Bloodshed skill tree. Many Must Fall allows you to stay in deception as long as you keep chaining kills whithin deception time limit. Every time you kill an enemy, you'll deploy a new hologram and 2 seconds are added to the deception time. It allows you to clear entire areas without breaking invisibility.





STARTING TVHM - From Lvl 32 to Lvl 36:
Counter Strike (CS) or Fast Hands. Counter Strike is the one of the top Skills for any melee Zero. The bonus is added to the base melee multiplier so the damage increase is immense. Unfortunately it is activated randomly after taking damage, and like all RNG skills, it's not something to rely on.
Fast Hands is an extremely useful skill, and it is needed for healthgating at higher levels. However Zero is a glass cannon and DPS skills are priority n.1. When your deception is in cooldown, and you are melee tanking with a rubi, CS is a life saver if you need to heal above healthgate. However being able to swap fast is also a life saver (for healing, or in FFYL for example) so both skills are equally good: it's just a matter of personal tastes and playstyle. You can take CS, or FH, or put 3 points in one skill and 2 in the other. Just remember to only put the minimum amount of 5 skillpoints on them because what you really want as soon as possible is ambush!

Recommended gear:
While you are still in normal mode, I suggest to get a lvl 30 Rapier and Pimpernel from DLC1. Remember to get the items in NORMAL mode! When you do the DLC in TVHM you definitely want them to be lvl 50: for this reason, always do DLCs after completing the main story.
A Rapier, with its 200% melee bonus, will help you keep Many Must Fall going. A Pimpernel might be the best FFYL weapon if you know how it works. Your low level Rubi will be your BFF: the melee damage will always be the same as well as its healing. Remember to never throw it away. You will definitely want a new Slag Evisceration Rubi at level 50, right before starting UVHM so pay attention to only take the quest "rakkaholic anonymus" ONLY after the Warrior is dead.
By now your Order is obsolete and you should replace it with a new roid shield. Farming vending machines is the fastest and easiest way to gear up. Remember to keep your tesla as much "up-to-date" as possible. Green and white items will be fine, as long as they are better than what you have equipped.


TVHM - From Lvl 37 to Lvl 41:
Ambush. Ambush is a MUST. Its bonus is Multiplicative and it synergize perfectly with backstab. It is activated when attacking an enemy from behind, so it will be there every time you get a backstab. It will also activate when an enemy is attaching your decoy so it will always be active when you are chaining Many Must Fall. Ambush is not shown in the video guide beause it is overlapped by backstab and it's really hard to show it on video.

Why not Fearless?
Fearless is good for a gun centered or hybrid Zero... But we are playing a pure melee Zero so this skill is basically useless for us right now. If our goal is to clear an entire area without breaking deception, Fearless is a complete waste of skillpoints. Ambush is multiplicative in the melee formula, it triggers all the time when we are in deception so it is a priority.

Recommended gear:
I warn you: Wilhelm will be a pain. You might want to kill him with guns so I suggest getting a Teapot from Tiny Tina. It is of greatest imporance to have a powerful tesla so farming the vending machines can make the difference for this fight. Why? Because your rubi is old and shooting it won't heal you any more. Rubi-tanking Wilhelm is impossible because all of his melee attacks will push you away, even if you are executing. The only way to heal is to throw Teslas while holding your Rubi, otherwise you'll be always below healthgate. For this reason your tesla need to be the highest level possible: if your tesla is weak, the healing won't be enough. If the fight is still troublesome, leveling up a little bit is also helpful.

TVHM - Level 42:
Death Mark (DM). Every melee attack will apply a Deathmark to the enemy. Only one Deathmark can be applied at a time. Deathmark will apply a 20% debuff to marked enemies, and will last 8 seconds.
Deathmark will shine later, when Death Blossom will improve it quite A LOT.
Rising shot is a great skill for both guns and melee: it will be our next choice. It is important to take DM first because it only costs 1 point ant it improves your damage significantly.

Why not Unforseen?
Unforseen is only good when you have nothing better to take... And everything is better than Unforseen. I admit, with a Shock Bone, an Infiltrator/Spy com, and Ambush doing it's thing this skill is amusing... But at endgame it will only kill skag pups and if you have MMF it is very uncontrollable and dangerous because you don't know where your next decoy will land and it will often explode barrels even at a relatively long distance.

Recommended gear:
I heartily recommend to not enter the preserve before reaching Level 42 or you might end up fighting bloodwing with melee (and it won't be pleasant experience). I suggest to get a few vladof sniper rifles of an adequate level, fire and/or shock element to soften Blodwing a little bit. The Octo is not too bad and the heartbreaker can be very helpful. If you have a slag transfusion it might be really nice.
I suggest to farm the vending machines for elemental immunity shields, they'll help a lot with bloodwing's elemental attacks. Even whites are great.

TVHM - From Lvl 43 to Lvl 46:
Rising Shot. Rising shot is a very nice skill. It adds damage to both melee and guns, and the damage can be stacked up to 5 times. This means it will be very helpful when chaining MMF kills and when rubi-tanking out of deception, allowing a better damage and a better healthgating.

Why not Unforseen? Unforseen damage scales poorly with the game, and at endgame it will only kill skag pups. It is also very dangerous if you are chaining MMF because you don't know where your next decoy lands and it will easily explode barrels even from long distance. However, I admit it might be amusing if you pair it with a shock bone, an infiltrator/spy class mod, and ambush. But it's only good if you enjoy staring at fireworks...

Why only 4/5? This is a personal preference: I think it is better to reach Innervate as soon as possible. The movement speed bonus is great and it stacks with followthrough for amazing MMF chains. The healing is also very useful, especially in those situations where you have no other healing sources, like the Vault for example.

Recommended gear:
Around level 46 it's bunker time. I tell you in advance, this can be an extremely hard mission, and it might be impossible if you don't have the right gear or your level is too low.
I suggest you to not start this mission if you are below level 46.

• After completing the mission "The Once and Future Slab" you'll get a blue roid shield as quest reward. It will probably be the best shield you'll find for the next few levels. If you want, you can try to farm the quest for an inflammable version of the shield, but it's not really important.
  
• Right before the Bunker, take the quest "Rocko's Modern Strife" but DON'T start it! Just take it. This quest will remove all the bandits from Thousand Cuts so it will be easier to farm the map.
  
• It is important to farm Thousand Cuts and not other places because the loot will be of higher level. Caustic Caverns is another great place to farm for both XP and gear.

The gear you are looking for is:

1. A roid shield better than what you already have, otherwise Roland's shield will do fine.
   
2. An high level, longbow or lobbed (better longbow) Tesla able to strip your best shield in 1 shot. Green rarity should be fine.
   
3. A shock Vladof or Dahl pistol. It will be very helpful to kill surveyors. High fire rate is best. Why shock? Because all surveyors have large shields, and corrosion does nearly nothing to them. On the other hand their HP is small so a shock pistol will do just fine. Alternatively a shock sniper should do a good job, but I prefer pistols because you are going to need your sniper ammo for bigger troubles.
   
4. Corrosive vladof sniper. You definitely want one of those to soften that ultimate Badass Constructor. Things can get extremely Ugly at this point. Oneshotting it is impossible, so you'll need a weapon able to soften it a little bit before going melee or even kill him from long distance if you don't feel like melee-ing it. Try to save as much sniper ammo as you can.
   
5. An amp shield and a sniper class mod, just in case everything goes HORRIBLY wrong with the Bunker...

TVHM - From Lvl 47 to Lvl 51:
Innervate. Innervate is the best of Zero's survival skills. Well he has 2 survival skills anyway lol. Innervate will give us an increased movement speed and constant healing while in deception. The more Deception lasts, the more is the healing. The movement speed bonus stacks extremely well with Followthrough and it will help quite a lot with MMF chaining.

Recommended gear:
For Saturn, I suggest to reach at least lvl 49. Like I suggested for Normal mode, farming Lynchwood is the best way to level and gear up: there are e few nice chests to check, and the baby maker is always a good Item if you manage to get it to drop.
I recommend to get a good Rocket Launcher just in case you need to second wind off a Saturn turret.
For the Warrior, melee is going to be hard without law+order. I suggest you to get a good jakobs sniper, a jakobs pistol and a jakobs assault rifle. Why? Because Jakobs weapons have the highest critical multiplier: they will do a good amount of damage on the warrior once you expose his critical spots. Torgue pistols are also decent because of the splash damage. Transfusion grenades just in case of emergency. An amp shield and sniper com might help but they are not necessary.



STARTING UVHM
After killing the warrior, you can farm for a few items to make UVHM less traumatic.
You should get:

• Slag Evisceration Rubi. It is n.1 priority.
  
• Order. Better if it has an elemental resistance.
  
• Law.
  
• Love Thumper. Better if it has an elemental resistance (inflammable is very helpful against Terramorphous).
  
• Slag Rapier. My favourite prefix is Rabid because more bullets = slag has higher chance to proc.
  
• Heartbreaker. This is a must against Terramorphous and it will help a lot for the first couple of levels in UVHM.
  
• Slag Transfusion or Slag betty. It will go perfectly with your Love Thumper. I prefer Transfusion for UVHM.
  
• Pimpernel. You never say no to a Pimp. Slag or fire are my favourite elements for starting UVHM.

With the aforementioned items, you should be fine for a couple of levels, however they won't last long.
If you feel weak and can't chain MMF with your found gear, I suggest you to change your mobbing build into the raiding build (see screenshot above), in this way you'll get Kunai and you'll be able to deal 60% more damage. However your deception will end with your attack so you need to hit and run and be very careful!
After completing Innervate and Rising shot, you should add 4 more points to either CS or Fast Hands (depends on what you choose earlier). Two Fangs is a good skill for Rubi slagging, but not in a melee build, and not if you are using a sniper rifle.
After level 57 you will have both Many Must Fall and Death Blossom and you'll feel much better! Kunai can apply Death Mark to multiple targets or stack the Death Mark debuff up to 80% on a single target (if Hotfix is active).
After that, your melee build is techically complete, and you can decide if you want to go for a bore or a boreless endgame build.

key skills for every Melee build are: Killing Blow, Execute, Backstab, Many Must Fall, Ambush, and Deathmark/Death Blossom (the two of which are a given together).

GENERIC LEVEL 61 MELEE BUILD



This is the highest DPS melee build available at lvl 61. The last 2 points can be put into Fearless, Two Fang, Headshot, or into whatever skill might be best for you, it's not important. I prefer to put them in Be Like Water, because it fits my playstyle, but it really doesn't matter.
Assigning the points to 2 Fangs can be helpful to have higher slag chances.
Realistically at 58 or higher, that is the best (and most accepted/standard) build for any and all melee Zer0s.

At 72, that expands to two different builds. One of which is with B0re, and B0re-less.


BORELESS GENERIC LEVEL 72 MELEE BUILD

GENERIC LEVEL 72 MELEE BUILD WITH BORE


Past level 58, the skills chosen are entirely optional. However, previous to that the skills are pre-chosen (nearly) and are based around maximizing damage according to Zer0's melee formula. After level 58 you can choose the skills you like the best freely, there is no rule. Just make sure to never take Grim because it will make your roid shield useless and it works against the melee playstyle.

What should I choose? Bore or Boreless?
Technically, Bore is one of the best Zero skills. It can deal a lot of damage especially to bots without the need of singularity grenades and it prevents bullet reflection from enemies and enemy shields (like Badassasarus, Dukino's mom, etc.) which is EXTREMELY useful in a melee build.
From a DPS point of view, Bore offers more advantages and versatility. There is no reason to take the remaining melee skills because they add very little to the overall damage and they scale poorly. However if you like the Idea of a full melee Ninja, boreless builds are challenging, but still perfectly viable.

Slot 1
Slag Rapier. Allows max melee damage. It's obtainable in DLC1 and it's a unique quest reward obtained from 'Message in a Bottle' quest, located in Hayters Folly. Always spawn with a blade accessory, boosting the weapons melee damage to 200%. A slag version is preferred in UVHM.
Alternative:
Law. The Law boosts melee damage by 100%. It's the best bladed gun available in the core game. If paired with the Order shield, any melee damage done is converted to health.

Slot 2
Slag Evisceration Rubi. Rubi is a unique quest reward obtained from 'Rakkaholics Anonymous' quest, and turning the mission in to Moxxi. No Accessories guaranteed. It will take a while to acquire the correct version Slag + blade accessory). This guns will be our main healing source: in fact, as all Moxxi weapons, it will heal by a percentage of the damage inflicted. Slag element is important in UVHM and this gun will be our Zero's main slag source.
Alternative:
Evisceration Grog Nozzle.The enemies damage reduction and the terrible DoT at high OP levels make the Rubi ineffcient. This gun is a quest item and it might be needed at OP8 because it heals a larger percentage than Rubi (65% to 12%). It is a quest item (NOT reward) from DLC4 and it was obtainable only once during the Loot Hunt event.

Slot 3
the 3rd and 4th slots are used for support weapons. Usually, for recovering from Fight For your Life, for extra slagging, or for extra healing, or to deal with flying enemies like buzzards and surveyors which might be difficult to reach with melee. The weapons used are extremely situational, so I'll just mention the most frequently used.
Unkempt Harold. The best prefix is Double Penetrating (DPUH). It is obtained from Torgue vending machines in DLC2, or as a rare drop from Savage Lee. It is one of the most powerful guns available in the game, but its main use for a melee Zero is as healing source. In fact this gun has an extremely slow bullet speed, so shooting an enemy and then quickly switch to a Rubi or Grog before the pellets reach the target, will fully heal. This is especially useful against raid bosses like Terramorphous and Voracidous.
Alternatives:
For healing purpose, any weapon with a very slow bullet speed can be used. I used a Blockhead once for example but in the end the DPUH is the most reliable emergency-healing weapon.
In the 3rd slot, other support weapons are used, especially by B0re ninjas. The choice goes to weapons that easily bore:
Pimpernel. It's a unique sniper from DLC1 obtained from the mission "Don't Copy That Floppy" located in Washburne Refinery. It's one of the most powerful weapons available in the game, however you need to know the sweet spots to make it effective.
Practicable Interfacer. It is a seraph shotgun dropped by Voracidous the Inivincible. The best variant has practicable prefix.
Tediore Plasma Casters. A special mention to Tediore reloads. Before OP levels, it was a fantastic second wind weapon: in fact, you can reload-throw it like a grenade: if the magazine is almost full, it deals immense damage, especially if the enemy is weak to its element. At OP levels, with enemy damage reduction, it's not as good as it was. The same applies to the legendary Baby Maker.

Slot 4
Norfleet. It's the most powerful rocket launcher available in the game and the best weapon for FFYL emergencies. It is a rare drop from Hyperious the invincible and Vermivorous. Fire, shock and corrosive norfleets are fine, slag element is not recommended.
Alternatives:
Topneaa. The Topneaa is a Vladof Etech rocket launcher. Its high fire rate and low ammo consumption make it the best FFYL weapon to use at non-OP levels. However its damage might not be enough to make it viable at OP8. It can be optained from any loot source.
PBFG. This is Norfleet's little Etech brother. It is a viable alternative to the Norfleet even at OP8. It can be optained from any loot source.
Badaboom. This legendary bandit RPG is dropped by King Mong.

SHIELDS:
Hide of Terramorphous. The Hide is a rare legendary Drop obtained from Terramorphous the Invincible. It has the highest Roid damage available in the game. It also have spikes and nova effects which are appreciated because they passively heal when holding a Rubi (in fact any damage done when holding a Moxxi weapon will heal you regardless of the source). The best hides have an elemental resistance and has a delay of at least 3.5 seconds. The best elemental resistance is grounded or inflammable.
Alternative:
Love Thumper. The Love Thumper is a unique quest reward obtained from 'Best Mother's Day Ever' quest located in The Highlands. This quest randomly drops from Stalkers after completing 'Stalker of Stalkers'. when the shield is depleted, it adds an explosive nova to all melee attacks. The nova inflict friendly fire, so it is not recommended for coop playing. It also has an extremely long recharge delay, so it doesn't need to be managed. However it will leave your health exposed the whole time. The best variants comes with an elemental resistance.
Order. The Order has a maximum roid damage comparable to the Love Thumper. It is a unique quest reward obtained from 'BFFs' quest located in Sanctuary. It is used in Coop instead of the Love Thumper if an Hide is not available. The best versions of this shield have an elemental resistance and a delay of at least 3.5 seconds.
Any Maylay shield with elemental resistance. I've seen a purple alkaline maylay shield with 1.4M roid damage, when the maximum damage for a perfect Love Thumper is 1.5M. Generic roid shields can be amazingly good! Always keep an eye on them and pick them up if they have an elemental resistance. They can be found in any loot source, Pyro Pete should drop maylay shields relatively often, together with other goodies, and he is easy to farm.

GRENADES:
Grenades are mainly used to strip your shield when roid bonus is needed. They are also used as healers when thrown while holding a Rubi. The only grenades that strip your shield without hurting your health are:
Longbow Stormfront (Longbow/Lobbed Tesla). The Stormfront is more powerful, but any Tesla can be as good as their legendary counterpart. Both Tesla or Stormfront need to be a bit specific, as it does need to be Longbow or Lobbed with a 0.0 fuse time. The Stormfront is a legendary grenade mod dropped from the Teenage Mutant Ninja Rats located in Bloodshot Stronghold. Longbow Teslas can also be found on vending machines and any loot sources. It must be powerful enough to strip your shield completely when you need roid bonus.
Alternative:
Chain Lightning. The Chain Lightning is a legendary/unique grenade Mod dropped from Sorcerers in the 4th DLC, with a 0.0 fuse time. However this grenade is very dangerous because it inflicts DoT and it needs to be paired with a grounded shield. It also wipe out a big chunck of health if used as shield stripper without holding a Rubi near an enemy. The advantage is that it regenerates ammo so it is easier to manage a fast recharging shield like Hide of Terramorphous. It also instantly heals if thrown while holding a Rubi.

RELICS:
Cooldown relic or Bone of the Ancients (non-shock). A better cooldown means more deception, more Kunai, more DPS, more survivability. More cooldown means more Executes overall, which is far better than any other relic in the game for Zer0. Shock variation of the Bone means that your grenades are boosted, and that means that they are deadlier to your health than any other bone. Avoid these at all costs. So: cooldown relics, and Fire/Corrosive Bone of the Ancients are the most preferable relics.
Strenght relics and Might of the Seraphs melee damage bonus is poorly added in the melee formula so they basically add hothing to the overall DPS. They are only used in very selected cases by pros for speed raiding, where everything ends in 1 deception.

CLASS MODS:
Blue Shadow Ninja (+6 backstab, +5 Killing Blow). This is the best class mod available for a Melee Zero in the base game. The blue com is the best because you definitely want +6 in Backstab, and Resurgence boost is not really needed.
Alternative:
Legendary Ninja. It will give bonus to all the Shadow Ninja skills, plus Ambush and Followthrough. This class mod is only dropped by Tubby enemies above level 62, it does not exist at lower levels. However, the Legendary Ninja is certainly better than the Shadow Ninja but not to the point to notice an big increase in DPS. The only noticeable difference is the boost to followthrough which is always good to have.
Legendary Hunter. The lack of melee damage boost is evident at endgame, but at lower levels (usually around 50) it can be good especially for the healing and cooldown bonus while mobbing.