granted, it looks more like a Duke3d enemy than Doom if I'm honest, but half of that bloody game's monsters are in the beastiary anyway lol
Personally I wouldn't accept a Duke 3D monster for Doom unless it were very carefully edited. There are quite a few things available on the site from waaaaaay back that I wouldn't be comfortable signing off on now, either.
Compare the shading very closely: It's all too obvious where one monster ends and the other begins. You should definitely shadow the legs a little more to match the torso. (Being a regular "frankenspriter" myself, I'm well aware of the shading problems that arise.) Other than that, they mesh well.
As per Gez's suggestion, some horns or spines would do a lot of good. Perhaps a hint of bloodstains here and there.
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