Every recent Pokémon generation has introduced a unique battle mechanic. Between Sword and Shield's Dynamax and Gigantamax forms, Sun and Moon's Z-Moves, and X and Y's Mega Evolution, traditional Pokémon battles have become more exciting and engaging. While some variation of the former two mechanics can be used by all Pokémon, only certain species can Mega Evolve - and that list isn't as long as some players might like.
Mega Evolution allows capable Pokémon to gain a new, temporary evolutionary form when holding the correct Mega Stone. Once per battle, a single capable Pokémon in the party can Mega Evolve for the duration. Mega Evolution lasts until the Pokémon is knocked unconscious or, unlike Gigantamaxing and Dynamaxing, the entire battle, if the Pokémon stays alive. Mega Evolution has appeared in X and Y, Omega Ruby and Alpha Sapphire, and Sun and Moon. It also appears in some spin-off games, but it's usually just a bonus there that's limited to a short list of species. In Pokémon GO, for example, there are only 10 Pokémon currently able to Mega Evolve.
There are 46 Pokémon total Pokémon capable of Mega Evolution, and there are 48 different Mega Evolution forms. All of these were introduced in Pokémon X and Y and Pokémon Omega Ruby and Alpha Sapphire, and all Megas are based on Pokémon that can't normally evolve further. Mega designs often exaggerate prominent features of their base-form Pokémon. For example, Venasaur gets a much bigger flower on its back, and Blastoise switches its two hydro canons out for a single, massive one. Mewtwo and Charizard each have two separate Mega forms, and the version they turn into depends and what Mega Stone they're holding.
All Pokémon Mega Evolutions & Required Mega Stones
Below is a list of every Pokémon in the series that can Mega Evolve, its typing and Mega Ability, and what Mega Stone is required to evolve it (via Serebii). Some Pokémon's types change when they Mega Evolve, which can switch up that Pokémon's strengths and weaknesses. Examples of this include Mega Charizard X and Mega Pinsir, among others. Mega Evolution also gives Pokémon special Mega Abilities different from their standard forms', which can offer players different boosts during battle.
- Mega Venusaur - Grass/Poison; Ability: Thick Fat; Mega Stone: Venusaurite
- Mega Charizard X - Fire/Dragon; Ability: Tough Claws; Mega Stone: Charizardite X
- Mega Charizard Y - Fire/Flying; Ability: Drought; Mega Stone: Charizardite Y
- Mega Blastoise - Water; Ability: Mega Launcher; Mega Stone: Blastoisinite
- Mega Alakazam - Psychic; Ability: Trace; Mega Stone: Alakazite
- Mega Gengar - Ghost/Poison; Ability: Shadow Tag; Mega Stone: Gengarite
- Mega Kangaskhan - Normal; Ability: Parental Bond; Mega Stone: Kangaskhanite
- Mega Pinsir - Bug/Flying; Ability: Aerilate; Mega Stone: Pinsirite
- Mega Gyarados - Water/Dark; Ability: Mold Breaker; Gyaradosite
- Mega Aerodactyl - Rock/Flying; Ability: Tough Claws; Mega Stone: Aerodactylite
- Mega Mewtwo X - Psychic/Fighting; Ability: Steadfast; Mega Stone: Mewtwonite X
- Mega Mewtwo Y - Psychic; Ability: Insomnia; Mega Stone: Mewtwonite Y
- Mega Ampharos - Electric/Dragon; Ability: Mold Breaker; Ampharosite
- Mega Scizor - Bug/Steel; Ability: Technician; Mega Stone: Scizorite
- Mega Heracross - Bug/Fighting; Ability: Skill Link; Mega Stone: Heracronite
- Mega Houndoom - Dark/Fire; Ability: Solar Power; Mega Stone: Houndoominite
- Mega Tyranitar - Rock/Dark; Ability: Sand Stream; Mega Stone: Tyranitarite
- Mega Blaziken - Fire/Fighting; Ability: Speed Boost; Mega Stone: Blazikenite
- Mega Gardevoir - Psychic/Fairy; Ability: Pixilate; Mega Stone: Gardevoirite
- Mega Mawile - Steel/Fairy; Ability: Huge Power; Mega Stone: Mawilite
- Mega Aggron - Steel; Ability: Filter; Mega Stone: Aggronite
- Mega Medicham - Fighting/Psychic; Ability: Pure Power; Mega Stone: Medichamite
- Mega Manectric - Electric; Ability: Intimidate; Mega Stone: Manectite
- Mega Banette - Ghost; Ability: Prankster; Mega Stone: Banettite
- Mega Absol - Dark; Ability: Magic Bounce; Mega Stone: Absolite
- Mega Latias - Dragon/Psychic; Ability: Levitate; Mega Stone: Latiasite
- Mega Latios - Dragon/Psychic; Ability: Levitate; Mega Stone: Latiosite
- Mega Garchomp - Dragon/Ground; Ability: Sand Force; Mega Stone: Garchompite
- Mega Lucario - Fighting/Steel; Ability: Adaptability; Mega Stone: Lucarionate
- Mega Abomasnow - Grass/Ice; Ability: Snow Warning; Mega Stone: Abomasite
- Mega Beedrill - Bug/Poison; Ability- Adaptability; Mega Stone: Beedrillite
- Mega Pidgeot - Normal/Flying; Ability: No Guard; Mega Stone: Pidgeotite
- Mega Slowbro - Water/Psychic; Ability: Shell Armor; Mega Stone: Slowbronite
- Mega Steelix - Steel/Ground; Ability: Sand Force; Mega Stone: Steelixite
- Mega Sceptile - Grass/Dragon; Ability: Lightning Rod; Mega Stone: Sceptilite
- Mega Swampert - Water/Ground; Ability: Swift Swim; Mega Stone: Swampertite
- Mega Blaziken - Fire/Fighting; Ability: Speed Boost; Mega Stone: Blazikenite
- Mega Sableye - Dark/Ghost; Ability: Magic Bounce; Mega Stone: Sablenite
- Mega Sharpedo - Water/Dark; Ability: Strong Jaw; Mega Stone: Sharpedonite
- Mega Camerupt - Fire/Ground; Ability: Sheer Force; Mega Stone: Cameruptite
- Mega Altaria - Dragon/Fairy; Ability: Pixilate; Mega Stone: Altarianite
- Mega Glalie - Ice; Ability: Refrigerate; Mega Stone: Glalitite
- Mega Salamence - Dragon/Flying; Ability: Aerilate; Mega Stone: Salamencite
- Mega Metagross - Steel/Psychic; Ability: Tough Claws; Mega Stone: Metagrossite
- Mega Rayquaza - Dragon/Flying; Ability: Delta Stream; Mega Stone: N/A - Rayquaza's Mega Evolution is based on knowing the move Dragon Ascent.
- Mega Lopunny - Normal/Fighting; Ability: Scrappy; Mega Stone: Lopunnite
- Mega Gallade - Psychic/Fighting; Ability: Inner Focus; Mega Stone: Galladite
- Mega Audino - Normal/Fairy; Ability: Healer; Mega Stone: Audinite
- Mega Diancie - Rock/Fairy; Ability: Magic Bounce; Mega Stone: Diancite
The Legendary Pokémon Kyogre and Groudon aren't like the other Mega Evolutions. They gain Primal Reversion forms, accessible when holding the correct Reversion Orb. Primal Reversion is technically a separate mechanic, as players can Mega Evolve a compatible Pokémon in the same battle, but the systems function almost identically. Currently, Kyogre and Groudon are the only Pokémon in the series that possess Primal Reversion forms.
- Primal Reversion Kyogre - Water; Ability: Primordial Sea; Reversion Orb: Blue Orb
- Primal Reversion Groudon - Ground/Fire; Ability: Desolate Land; Reversion Orb: Red Orb
Source: Serebii