The Goosebumps book with a bad-luck causing sponge monster.
Katrina "Kat" Merton and her family have moved to a new house, where their dog quickly discovers a strange sponge, which seems to have eyes, under the sink. But as a series of misfortunes begin to plague the family, Kat's brother Daniel discovers the sponge's true identity as the Grool, a monster that feeds on bad luck, and cannot be gotten rid of until its current owner dies. Now, Kat and Daniel must try to figure out a way to safely beat the Grool's powers.
It was adapted into the fourteenth episode of the first season of the 1995 TV series.
The book provides examples of:
- Absurdly Spacious Sewer: Kat goes down a pothole in the street to encounter this while searching for the Grool.
- Agony of the Feet: Daniel's friend Carlo tries to study the Grool, but it's cut short when he steps in the wrong place and a nail goes through his foot.
- Bad Luck Charm: The Grool brings bad luck to whomever finds it, up to and including death.
- Big "SHUT UP!": Kat yells this twice at the Grool when it snickers after her first failed attempt to kill it.
- Bloodier and Gorier: There is a lot more bloody violence than usual for the series, including someone stepping on a nail and bleeding from it.
- Clingy MacGuffin: The Grool only moves on to a new owner when the previous one dies. Attempting to give it away will result in automatic death for its owner within one day.
- Cool Car: Kat's aunt Louise drives a bright yellow convertible, which is one of the reasons why Kat really admires her.
- Door Slam of Rage: Kat does this in Daniel's face when he tricks her into thinking they had school today even though they had the day off.
- Dramatic Irony: When she brings an injured Ms. Vanderhoff to the school nurse, Katrina is told that she's been very helpful. Katrina herself notes that this isn't true, because people kept getting hurt thanks to her and the Grool.
- "Eureka!" Moment: Daniel is looking through the Encyclopedia of the Weird again, and he again reads aloud how the Grool cannot be killed with force nor violence. This gives Kat the bright idea to do the opposite of those things. Sure enough, it works.
- Evil-Detecting Dog: Kat's dog Killer starts growling at the space under the sink, which happens to be home to the Grool. And he later does the same when he finds the Lanx in a cupboard right next to the sink.
- Fingore: When Kat tries to have her teacher examine the Grool, it causes Ms. Vanderhoff to slam her fingers in the drawer of her desk.
- Foreshadowing: In the Encyclopedia of the Weird, it mentions the Grool is also closely related to a creature called the Lanx, a potato-like creature with fangs, which is reportedly much more dangerous because it sucks the life-force out of you. It seems like a random fact until at the end of the book where Kat finds Killer carrying the Lanx.
- The Glomp: When Katrina thinks that she found the Grool after losing it, which could have caused her to die, she excitedly hugs Daniel's friend, Carlo, tightly. Carlo does not appreciate this, and tells her to get off him.
- Here We Go Again!: The book ends with Kat discovering a potato with a mouthful of teeth — matching the description of a Lanx, an energy-draining monster found in her brother's Encyclopedia of the Weird book earlier.
- Imagine Spot: When she worries that she might die because of losing the Grool, Kat imagines her brother walking to school alone, her parents crying their eyes out, and her aunt wondering why she didn't believe her. These make her more determined to get the Grool back.
- Keep Away: When Kat finds that a duo of teenagers have the Grool, she demands that they give it back to her. So they tell her to get it herself with this trope. They do this for ten minutes with her unable to catch it, so she just gives up and decides to let the bad luck do the job for her.
- Logical Weakness: Since it feeds on bad luck and negativity, showing it kindness weakens and eventually kills the Grool.
- New House, New Problems: The family moves into a new house that's home to a monster that causes bad luck.
- No Name Given: The two teenagers whom pick on Daniel and find the Grool only has one of their names revealed; Dave. The other boy is only referred to as "the blond boy."
- Our Monsters Are Weird: The Grool, a monster that looks like a sponge but is alive and causes (and feeds on) bad luck.
- Out of the Frying Pan: After getting rid of the Grool, Kat finds a Lanx, which causes instant death if it latches onto you by draining all your energy.
- Playing Possum: The Grool does this a few times, pretending to be a normal sponge around people other than Kat and Daniel so nobody will realize its true nature.
- Phony Psychic: What Kat's Aunt Louise turns out to be. She knows about astrology and tarot cards, but when Kat shows her the Grool hoping that she can figure out more about it, Louise is clueless.
- Punctuated! For! Emphasis!: At one point when asking Daniel where Carlos is, Katrina repeats slowly, "Where...is...Carlos?"
- Reverse Psychology: How do the protagonists destroy a Bad Luck Charm that feeds off of negativity? By literally killing it with kindness.
- Stern Teacher: Ms. Vanderhoff, Kat's intelligent but strict teacher. According to Katrina, anyone who goofs off or talks out of turn stays after school for a week. She also apparently has no sense of humor.
- Stunned Silence: Daniel and Carlos have a case of this when Kat is explaining to them how the Grool was able to be killed through her shows of compassion towards it.
- Tears of Fear: Kat starts to do this when she starts to think that she's lost the Grool forever, which means she will die. But she stops herself because she didnt want Daniel nor Carlos to see how scared she was.
- Teens Are Monsters: Two teens show up to cause problems for the main characters. When they encounter Carlo, they dare him to race them, and he collided with a tree which caused all of them to laugh at him. And when they find the Grool, they play catch with it and taunt Kat to get it.
- Watch Out for That Tree!: When riding on his bicycle as part of a dare, Carlos hits a tree which sprains his knee. It also sends the Grool flying off for teenagers to find and play catch with.
