Goopling

Goopling (Aka: Small Goop) is a small blob of the same liquid as Goop, it is small because it was made to go under Goop's containment room doors, it is an obligate parasite meaning it requires a host to survive, it is completely harmless unless too many of itself fuse inside its host, it enters a host through whatever hole it can...

Method of killing
It will go inside a creature and fuse with other Gooplings until it becomes big enough to cut its host's organs

Trivia
Gooplings are based on Light Latex Blobs

Gooplings are the first obligate parasites made by Peter