The Mutant Bat is a common Earth bat, which was mutated by Dr. Animo's Trans-modulator prior to Ben 10 vs. the Negative 10: Part 1.
Its body is very similar to a lizard's body but it has bat-like features. it has a wide mouth with a few small fangs. It has four small, red eyes. it has four big, bat-like ears and a horseshoe-like nose. Its neck and chest is covered by dark brown fur. Its body is grey and its legs and tail are light brown. It has claws on its wings and a spike on his tail.
The mutant bat is very strong and can fly. He is resistant against Diamondhead's sharp crystals. It can hang up-side down, like normal bats. It can also create powerful sonic waves.