>>52709597Every Pokémon has a Tera Type in addition to their regular type(s). In-game this usually matches one of the types they already have, but eventually you can change it to whatever you want.
The Tera Type doesn't do anything until you Terastalize. You can Terastalize once per battle (in-game you have to recharge it at a Pokémon Center), any Pokémon can Terastalize, they don't need to hold an item or anything. It activates at the start of the turn and changes the Pokémon's type(s) to its Tera Type.
The benefit of this is that you gain the Tera Type as a new STAB and are treated as that Type for defense, AND you don't lose the STAB on your original typing. If your Tera Type is the same as a Type you already are, then the STAB bonus goes from 1.5x to 2x damage. So a Tera Fire Charizard would do 33% more damage with Flamethrower and take less damage from Rock, but it would also lose its Ground immunity. It's also important to note that Pokémon stay Terastalized for the whole battle, even after they switch out.
Hidden Power is more or less replaced with Tera Blast, which by default is an 80BP Normal-type move but when you Terastalize it changes to match the Pokémon's Tera Type, and ALSO becomes either physical or special depending on which stat is higher.
In competitive people tend to use it to shore up a Pokémon's weaknesses instead of just stacking on more damage, but it depends on the Pokémon. A lot of the controversy comes from the idea that it makes offensive Pokémon harder to check - Gyarados can use Tera Ground to turn its 4x Electricity weakness into an immunity and benefit from STAB Earthquakes, for example - and getting one "free" turn from a super-effective hit becoming a resisted one can swing a whole battle.
It's undeniably more balanced and complex than any of the battle gimmicks before it, it has real potential downsides and trade-offs but that just makes it harder to predict and compfags hate that.
