Mutant Radioactive Pet Barrel
“This barrel wasn't always this way. Before its numerous transformations, it was just your average cask, filled with nuclear waste of unrivaled toxicity, hidden deep underground in the middle of nowhere. The serial number engraved on the lower edge reads 5LY14, but some sharp-witted worker wrote over the 5 and 4 with permanent marker so it now says 'SLYMA.'”
Slyma is a sentient, radioactive barrel. It has 4 limbs and is quadrupedal. It has an eye in the center of the barrel, with teeth covering the perimeter of its "mouth." Slyma also has what appears to be molten lava in its mouth, and is able to spit it out as an attack method.