User blog comment:Hidden Scorpius XI/Another problem with Vol. 2 (In my opinion)./@comment-10380701-20150522232017/@comment-25555436-20150522234725

The Creep can still be considered a corrupted animal though. There are a number of explanations for it, though all hypothesis.

1-It's a corrupted mutant frog.

2-It's a corrupted ancient animal, from very very long ago. However, as those animals stayed in the same environment for centuries, which never truly changed over these years, they barely, if ever, evolved and as such still keep their appearance that is pretty much nothing like a modern animal.

2.1-And possibly, the original animal died long ago, went extinct, as the environment did change and they couldn't evolve fast enough. However, the Grimms of that species did survive, as they can live for long and don't need to eat or anything. However, because there weren't really any dangers of any sort in that environment for centuries, they never experienced anything that would force them to become stronger, one way or another, which is why they look as armored as a normal Ursa.

3-The Grimm can be corrupted versions of multiple animals at once, possessing traits of both, similar to the Aragami from God Eater (but thankfully(?) without the "can eat anything" part). The Creep is just one example.

4-It's a Frogzard.