Lanx

The Lanx is a mythical creature introduced in the thirtieth Goosebumps book, It Came from Beneath the Sink!, and its accompanying television adaptation.

History
The Lanx is a cousin of the Grool. They are both ancient, mythical creatures. Both creatures feeds off their victims' energy, but the Lanx is supposedly far more dangerous than its cousin. The Lanx latches onto someone until it drains all of their energy.

The Lanx is first referenced about halfway through It Came from Beneath the Sink!; the characters find information about the creature in the book Encyclopedia of the Weird. However, the Lanx doesn't appear until the end of the story. After defeating the Grool, Katrina Merton's dog, Killer, brings home a Lanx.

Physical appearance
The Lanx resembles a potato, except it has a mouth and jagged teeth.