Protean

Protean changes the Pokémon's type to that of its previously used attack.

Game descriptions

X, Y, O.Ruby, A.Sapphire:Changes the Pokémon’s type to the type of the move it’s using.
Sun, Moon, Ultra Sun, Ultra Moon:Changes the Pokémon’s type to the type of the move it’s about to use.
Sword, Shield, B.Diamond, S.Pearl:Changes the Pokémon’s type to the type of the move it’s about to use.
Scarlet, Violet:Changes the Pokémon’s type to the type of the move it’s about to use. This works only once each time the Pokémon enters battle.