Sponge Monster

Sponge Monster is the name of a sponge with fangs introduced in It Came from Beneath the Sink.

Summary
The monster is found under the new house's sink and causes her and her brother bad luck. He is buried in the back yard by Kat but her brother's friend says that if the founder kills it, they get killed too. So they go to unbury it and find out it turned all of the plants and grass outside a gray-ish color. At the end of the episode, the sponge is defeated by the sign of happiness and luck and is later placed in Kat's bedroom and forced to listen to the Goosebumps theme song forever.