Demon hair?
Demon hare.
World-ending demon hair.
IIRC before I released my own mod I was working on the Burning Legion race and had worldgen crash issues that I couldn't quite figure out - so I reached out to Enemy post for help.
He found out it was some issue related to their hair tissues that was causing crashes in worldgen.
So yea. Demon hair was too awesome for most worlds to handle and caused implosions.
I once made a mistake modding T.Rexes in and the resulting creature was a blob of multiple whole tyrannosaurs mashed together.
I tried to make Terminators and got a metal skeleton with eye and brain tissue stretched over its body.
I attempted making a world where anyone killed would come back to life. However, I neglected to heal them of the injuries that killed them, so anyone who died would perpetually crawl around dying over and over.
That first one reminds me of a succession fort - I forgot which one, but IIRC by mistake they spliced the raws of a peregrine falcon and some other bird, leading to fractal bodies.
I love the terminator bit - it sounds incredibly gruesome. Wish I could draw it.
I had that issue too with my resurrection spell since I didn't add a milisecond transformation to remove the wounds - when I first tested it out, I went to a tomb and resurrected one of the dead bodies there. The guy rose up...missing all flesh, skin and, well, everything else except bones, and promptly bled to death a single tic later.