What is Terastalization and how does it work?

As has been typical of the last few generations in Pokémon, Scarlet and Violet introduced a new game mechanic, Terastalization. You can do it once per battle and must recharge before doing it again.

What is Terastalization?

Terastalization is a mechanic in Pokémon Scarlet and Violet that allows your Pokémon to change its type or amplify the one it already has.

What does it do?

Every Pokémon has a Tera-type, which is often the same as its type, or one of them in case of it having two, but it can also be a completely different type.

When you Terastalize your Pokémon, it will change to its Tera-type, changing its Resistances and Weaknesses to those of the type it changed to, overwriting those it previously had if they were different; changing to a different type than the original will mean that the Pokémon will gain the Same Type Attack Bonus from that type (1.5x the damage) while Terastalizing to the same type will give an extra boost (2x the damage).

Additional Effects

Terastalized Pokémon cannot have their type changed during a battle; for example, moves like Soak won't take effect on Terastalized Pokémon; the same goes when your Pokémon uses moves like Burn Up or Double Shock, which normally removes the Pokémon's Fire or Electric-type after using it, Terastalized Pokémon will keep their Fire or Electric-type respectively.

While you can Terastalize only once per battle, you can do it at any point, and if during the battle you have to switch out, the terastalized Pokémon won't lose the effect, so if you take it out again during the same battle, it will remain Terastalized.

Tera-types

There are 19 Tera-types, one for each type, and the Stellar Tera-type introduced in the Hidden Treasure of Area Zero DLC, which is good in some special cases.

Regular Types

As mentioned previously, when Terastalizing, the Pokémon will gain all the Resistances and Weaknesses of the type it is changing into, losing the ones it already had in the process.

Attacks of the same type as the Tera type will do 1.5 times the damage they would normally do if the type was different.

Attacks of the same type of the Pokémon will do 1.5 times the damage they would normally do if the type was different, even if they are Terastalized into a different type.

If the move coincides with both the Pokémon's Type and its Tera-type, it will do twice the damage it would normally do if the type was different.

Stellar

Stellar Tera-type is a special case, as it does not change your Pokémon's resistances or weaknesses.

On regular battles, you get a boost on your moves once per type, meaning that if you have two moves of the same type, only the first one you use will be boosted.

The Pokémon will receive the same boost it normally gets from its type, and adding the Stellar Terastalization, it will receive the extra boost only once.

Moves like Tera Blast and Tera Storm will be Super Effective on Terastalized Pokémon, regardless of their type.

The rule of once per type does not apply during tera Raid Battles, nor if the Pokémon is Terapagos.

How to change a Pokémon's Tera-type

Throughout your journey, you'll run into Tera shards of different types, often dropped in the ground or as rewards from Tera Raid Battles. You can use these to change your Pokémon's Tera-type by talking with the cook at the eatery in Medali, but only after you have already defeated Larry, the Gym leader; you need 50 Tera shards of the type you want your Pokémon to change to.