I couldn't tell if it was a rock or not, mainly because of the shading just being some time of filter(?)...
I could do it for you but I'd need some more in-depth details, like size, color, pose if you have one in mind... Because I could just draw a rock with a face on face... Also, would this monster be completely evil, trying to be scary but can't, or just plain chibi cute?
It looked like a rock until I started screwing around with the tools in photoshop lololol.
Umm, I want him fairly large(hes a boss character, but you probably can't see that from my pic), mostly grey with some occasional magma oozing out and the pose will be him lunging towards the screen/ trying to grab someone. It will also be completely evil and scary, but I failed at that too lolol. If you could do it, that would be great.