Slime

Slimes - also commonly called ooze - are common types of monsters in many fantasy roleplay games. True to their name, they don't usually have any distinct shape and appear as large masses of gelatinous fluid. Slimes and oozes vary between mediums, with some being intelligent and capable of assuming basic shapes with others being nothing more than brainless piles of goo that dissolve whatever matter becomes enveloped by their bodies.

Shoggoths
First appearing in H.P. Lovecraft's At the Mountains of Madness (1931) Shoggoths are a race of amorphous, shapeshifting protoplasm which were bio-engineered by the Elder Things, a race of prehistoric advanced alien colonists. The Shoggoths were created after the Elder Things lost their original slave-species of humankind and long after the star-spawn of Cthulhu forced the Elder Things to live in Antarctica. The Shoggoths themselves came to hate their masters and revolt against them, leading to the extinction of the species.

Nearly a billion years later the Shoggoths antagonize scientists who came to Antarctica from Miskatonic University after their discovery of the Elder Things's ruins. Shoggoths appear to be single-celled organisms who can shapeshift to acquire whatever body parts they desire but who naturally appear as mounds of slime with random, swirling features.

The Blob
The Blob is a monster first appearing in the 1958 monster movie of the same name. The Blob is a magenta gelatinous creature made of some sort of biological acid which it uses to consume biological matter which it intakes, expressly through a carnivorous diet. It comes to Earth after a meteorite falls in Pennsylvania and the creature goes on a killing-spree before it's revealed that it's weakness is the cold which freezes it's body.

Using fire-extinguishers the Blob is stopped, captured and transported to the Arctic to be contained.