Terastal

Terastal is the new battle mechanic in Pokémon Scarlet & Violet. This mechanic can be used once per battle and when activated, creates a jewel and luster around each Pokémon

Each Pokémon in Paldea can Terastallize and each Pokémon has a special Tera Type. When it is Terastallized, it will change its type to its special Tera Type. These are not specifically set by species, with the Tera Type being either of its standard types, but you can find different Tera Type Pokémon through Tera Raid Battles.

Tera Types cannot be passed down by breeding, with the hatched Pokémon's Tera Type being based upon its own types with a 50/50 chance of either type, and any Abilities or moves that would change the Pokémon's type, either the user's or an opposing Terastallized Pokémon, will not change the type of that Pokémon.

You will need a Tera Orb in order to Terastallize a Pokémon and, in Paldea, you will need to recharge the Tera Orb after use by either touching crystals of Terstal Energy or going to a Pokémon Center.

You can also find special Wild Tera Pokémon throughout Paldea. They can be seen with a special aura and will Terastalise in the battle with you but their Terastalisation will break if enough damage is inflicted.

When your Pokémon Terastallizes, it changes its entire type to a single pure type Pokémon matching its Tera Type. With this, its moves get a Tera Boost. If the Pokémon is no longer of its original types, those types still get the STAB of *1.5, and the new Tera Type also gets the STAB of *1.5.

If however, the Pokémon Terastallizes into a type which is the same as one of its original types, then the boost on moves of that type is *2 instead. If the Pokémon also has Adaptability as its Ability, then the STAB is *2.25

Low Power Boost

There is another boost that happens with Terastallizing. If you use a move that matches your Tera Type while Terastallized which has a Base Power of under 60, then it will be raised to Base Power of 60. There are a few exceptions.
First the move can't be a multi hit move or priority move. If the Ability Technician is in use, it must still be under 60 after Technician has been affected. The following moves are also unable to be boosted up when their damage is factored in.

Ineligible Moves

Name	Type	Cat.	PP	Att.	Acc.	Effect
Crush Grip			5	--	100	The target is crushed with great force. The more HP the target has left, the greater the move's power.
Dragon Energy			5	150	100	Converting its life-force into power, the user attacks opposing Pokémon. The lower the user's HP, the lower the move's power.
Electro Ball			10	--	100	The user hurls an electric orb at the target. The faster the user is than the target, the greater the move's power.
Eruption			5	150	100	The user attacks opposing Pokémon with explosive fury. The lower the user's HP, the lower the move's power.
Flail			15	--	100	The user flails about aimlessly to attack. The less HP the user has, the greater the move's power.
Fling			10	--	100	The user flings its held item at the target to attack. This move's power and effects depend on the item.
Grass Knot			20	--	100	The user snares the target with grass and trips it. The heavier the target, the greater the move's power.
Gyro Ball			5	--	100	The user tackles the target with a high-speed spin. The slower the user is than the target, the greater the move's power.
Hard Press			10	--	100	The target is crushed with an arm, a claw, or the like to inflict damage. The more HP the target has left, the greater the move's power.
Heat Crash			10	--	100	The user slams into the target with its flame-covered body. The more the user outweighs the target, the greater the move's power.
Heavy Slam			10	--	100	The user slams into the target with its heavy body. The more the user outweighs the target, the greater the move's power.
Low Kick			20	--	100	A powerful low kick that makes the target fall over. The heavier the target, the greater the move's power.
Reversal			15	--	100	An all-out attack that becomes more powerful the less HP the user has.
Water Spout			5	150	100	The user spouts water to damage opposing Pokémon. The lower the user's HP, the lower the move's power.

The Stellar Tera Type is the 19th Tera Type that can be found when going through the depths of Area Zero. This Tera Type doesn't change the Pokémon's weaknesses or Resisances but gives a one-time per type per battle boost to moves in standard battle, and constant in Tera Raid Battles.

With this Tera Type, Tera Blast is always super effective against Terastallised Pokémon but lowers the user's Attack and Special Attack.

There is however a way to change a Pokémon's Tera Type. After completing the Medali City Gym, go to the restaurant in Medali where you can exchange 50 of one type of Tera Shard to get a meal that will change your Pokémon's Tera Type to that type. These items can be found randomly on the ground throughout Paldea or as Raid Rewards