What is the game when people turn into animals?

You're likely thinking of the game Werewolf, also known as Mafia. It's a social deduction game where players are assigned secret roles, including werewolves who try to eliminate villagers, and villagers who must figure out who the werewolves are.

While players don't physically turn into animals, the werewolves are often represented by animal imagery or names, and the villagers are trying to "hunt" them down.

Is that the game you were thinking of?