Half an hour speed paint of a new IBSFA monster....well, technically a monster.

A prototype war monster created before the terrifying Tarrasque was initially nicknamed the "King of Monsters", however due to a flawed creation process all of the first and only batch of this monster came out about the size of a mouse and completely harmless.

As a total failure as a species of war, the whole batch was flushed down the sewers and thought to have perished in the deep dark of the unfortunately brown river, until a few thousand years later when a band of brave adventurers exploring the ruins accidental fell into the remains of the sewer system and discovered a whole colony of tiny little things. Found to be harmless, the little guys when brought back to civilization and given some very extensive baths before being sold as exotic pets.

It was only after a few years and a lot of frustration from scholars and breeders alike that it was discovered that one, the Zillas don't have any sort of gender nor procreation process, and two, they are also practically indestructible and immortal, concluding that these little monsters rescued from the ancient sewers where not a colony of offspring but the actual failed batch of monsters that saw themselves flushed down the bog thousands of years ago.