The Whack Rats are supporting antagonists in Season 12: Prime Empire of LEGO Ninjago: Masters of Spinjitzu. They are allies of Unagami and his army they are also the arch enemies of the Prime Empire racers.
The Whack Rats were created when prime empire was created they were given the role of enemies in the game when the game was shut off the rats become affiliated with Unagami and began working for him.
Season 12: Prime Empire
The Whack Rats are major participants in the speedway race in prime empire like some other racers the rats use cheating to win one of the rats Richie (Hauser) becomes a recurring antagonist in the season assisting Unagami in his plans and fighting and deceiving the ninja on a few occasions in episode 6 Richie goes with the Red Visors to attack the ninja and Okino the Red Visors get defeated while Richie is captured by the ninja he tries to tell the ninja that he can help them find an artifact but it is later revealed to be a trap with Richie being revealed to have actually lied to them when Unagami's army goes to earth the rats also go there they are seen causing chaos in ninjago city by throwing bombs at people the ninja take Richie's vehicle away from him later when Unagami redeems himself and sets all the NPC's in prime empire free the Whack Rats decide that prime empire is a better place to live than on earth so they along with some Red Visors and Aerial Drones go back to prime empire.