STABmons is the metagame where Pokemon have access to moves that match their type even if they can't normally learn them! Using Eevee as an example, it can now learn every Normal type move. This also applies to Pokemon that change type(s) during evolution. That means Eevee can pass Normal moves to all its Eeveelutions. New moves are "taught" as if they were TMs.
Mechanic: Pokemon can learn any move that matches their typing. This transfers with evolutions, so if a Normal-type evolves into a Psychic-type in the game, you can teach the Psychic-type Pokemon any Psychic and Normal moves.
Clauses: OU clauses
Bans: OU banlist + the following [reasoning in brackets]
Because a lot of Pokémon can learn powerful new attacks that they previously couldn't use, STABmons is can be a fast-paced metagame. Examples of strong wallbreakers include Water Spout Keldeo, V-create Mega Charizard X, and Boomburst Sylveon. Setup is also very common. Dragon Dance Garchomp, Tail Glow Yanmega, and Z-Trick-or-Treat Hoopa-U are good examples of Pokemon that can abuse setup moves.
People rely on the combination of Fake Out + Extreme Speed (nicknamed FakeSpeed), which is usable on any Normal-type Pokemon such as Diggersby, Mega Lopunny, or even Pixilate Sylveon, to check setup. This one-two punch delivers a lot of damage all before the target can retaliate, making FakeSpeed a reliable and important element to keep dangerous threats in line.
However, many Pokémon also get defensive or utility-based upgrades. For instance, Celesteela can now Roost its health back, Defog away hazards, and burn physical attackers with Beak Blast, and Ferrothorn can Spore, Sap Strength, and Anchor Shot. This means that many fatter or more balanced archetypes are still extremely viable.
Q: Do Mega Pokemon transfer types to their base form? For example, can I transfer Dark moves from Mega Gyarados to regular Gyarados?
A: No, any new moves must be "taught" outside of battle like a TM. Gyarados is only ever Water/Flying outside of battle so it cannot get access to Dark moves.
Q: What about forme changes?
A: Similarly to how megas work, any forme changes that happen during battle won't transfer moves. Castform is a good example of this, as it only changes type with the ability Forecast while in effect during a battle. Any forme changes that happen outside battle will transfer types, with a few exceptions. See the Forme Type Changes tag below for the full list.
Q: Do Alola formes trade types with their normal counterparts (e.g. can Alola Ninetales learn all Fire, Ice, and Fairy moves)?
A: No. (There are a few Alola formes that evolve from non-Alola Pokemon and carry over their old type. See the Evolution Type Changes tag.)
Q: What about unreleased moves such as Light of Ruin?
A: Only released moves are available.
Q: Why can't my Dark-type Tyranitar use Hyperspace Fury or Dark Void?
A: Hyperspace Fury is coded to only work on Hoopa-U and Dark Void is coded to only work on Darkrai. STABmons only changes the access to new moves, it doesn't change how their coding works.
Q: Can Chatot still use Chatter even though that move is banned?
A: Yep! The banned moves only apply to Pokemon that don't normally learn them.
Q: Can I teach Bloom Doom, a Z-move, to my Grass-type?
A: No. Z-moves are only available at the time of use with a Z crystal and thus cannot be "taught" outside of battle.
Q: Why was X banned?
A: Check the links above in the banlist for reasons (where you can find them).
Playability: STABmons is playable on the main PS server or ROM.
Council: Betathunder Funbot28 Official Fissure ihhca Eevee General
Viability Rankings: Post #2
Sample Teams: Here
Role Compendium: Here (under maintenance)
Evolution Type Changes:
The following Pokémon change only during battle and thus don't transfer types according to the rules of STABmons:
Castform, Meloetta, Darmanitan, all Mega formes.