Monster Blood is a sentiant thick green slime with magical properties that appears as an antagonist in several Goosebumps books.
The green slime makes its when it is discovered in an old toy store in a dusty metal can which is opened by the main protagonists, Evan Ross and Andy. Soon afterwards, Evan's dog named Trigger eats some and grows very large. The Monster Blood itself grows larger and larger as the story progresses, eating several objects and even a couple people. It is later revealed that the Monster Blood's abilities were caused by a spell cast by a witch named Sarabeth.
Monster Blood II
Monster Blood reappears when Evan initially has a dream involving his dog Trigger. In the dream, he notices Trigger has eaten Monster Blood. Soon after having this dream, only now in waking life, Cuddles the class hamster, eats some Monster Blood. Evan is then forced to eat some also in order to combat the gorilla-sized hamster. At the end, when the Monster Blood's expiration date kicks in, Andy gives Evan some more from Europe and Cuddles eats some more and the book ends.
Monster Blood III
Monster Blood returns when Evan and Andy come up with a plan to get Kermit back with Monster Blood for getting on their nerves. Their plan goes wrong and Evan accidentally swallows some and grows at least two stories high. He then sticks Conan up a tree and plays a game of softball, though this doesn't last long, as he is a highly visible and unusual sight at his new height, attracting public attention. The police and fire department soon come, thinking he is an alien threat. Eventually, Kermit makes a formula at home which causes shrinking, allowing Evan to drink it. Evan wakes up the next day and is the size of a mouse.
Monster Blood IV
In the last book in the Goosebumps book series, Monster Blood comes in a can, but is blue, and multiplies when exposed to water. The blood is also carnivorous, evil, and has fangs. This blood is actually not a toy at all, but an aquatic military super weapon. The blue Monster Blood also makes a person multiply, when someone eats it.
Monster Blood for Breakfast!
This version of Monster Blood is a "12 Hour Trial Strength" version, and it comes in a plastic egg. A character by the name Matt Daniels, grow about nine feet tall. The Monster Blood follows him to HorrorLand where it sucks up Sheena Deep and a Horror named Byron who saved Matt and Sheena's brother, Billy.
Goosebumps (TV Series)
Monster Blood appears in the Goosebumps TV series, in the episodes "Monster Blood" and "More Monster Blood", where airline food makes it shrink. It will only stop growing when it is put back in its jar. If a person eats it, they had better make sure some of it gets on their clothes; without doing so, their clothes will rip off if they continuing growing.
Goosebumps: The Game
Monster Blood appears in the videogame when you encounter it in the tunnels beneath the Dead House, then a second time at the entrance to the attic.
Initially, Monster Blood appears as a typical novelty "slime" toy, such as Mars Mud or Silly Putty, and comes in a small metal can. It glows in the dark and bounces like a ball when it is thrown. However, it is also alive, able to move on its own and consume anything it can envelop, including people and animals, to add to its mass. In addition, any living thing that consumes Monster Blood will grow several times their original size.
Asides from the ordinary Green Blood, there actually are also other variations of slime that are used in a similar fashion:
- Purple Peanut Butter, which has the opposite as the original (Shrinks the consumer instead of enlarging him/her), It gets its name from its color and peanut butter-like smell.
- Blue Monster Blood, Which multiplies whenever it makes contact with water. Anything that consumes it multiplies and becomes meaner.
- "12 hour Trial version", which basically was a "watered down" version of the original effects.
- "Vampirism Goo" (also known as Vampire in a Can): A red Monster Blood-like goo that turns whoever consumes it into a vampire. It actually has no legitimate relation to Monster Blood, but it works in a fashion much similar to it.
- The Monster Blood is the first antagonist in the series to appear in a sequel and become a recurring character.
- The Monster Blood was the first antagonist in the series to not speak.
- The green Monster Blood shares many similar qualities with the alien from The Blob and the 1988 remake of the same name.
- The Monster Blood shouldn't grow after the first book since Sarabeth, the witch who cursed the Monster Blood, dies at the end of the end of the book. This causes the Monster Blood to shrink. This means that the books Monster Blood II, Monster Blood III, and Monster Blood for Breakfast! shouldn't grow or be able to make things giant. Even if Sarabeth curses all of the Monster Blood in the world, all of the Monster Blood would shrink away.
- Monster Blood was speculated to appear in the 2015 film Goosebumps as one of the monsters unleashed by Slappy. However, Monster Blood was only mentioned in the film.