I don't know if I discovered it on IMVU, but I sort of did in terms of sharing it with my partner at the time as a thing that came out of the blue - kinda got hooked on it from there. Likewise in later years it's allowed me to kind of enable the kink a little more on IMVU, since it's hard to come by art and it's purely a fantasy/fiction thing.
Specifically, zombies and necro. I just find the prospect of spooky smut and a little horror with the horny to be incredibly fulfilling. Anywhere from very willing to much less consensual, clean or 'gross'. Is it fucking weird? Yes. But I like it and I kinda like that it's a fictional kink. Though, I wouldn't say no someone dressing up a zombie IRL to roleplay it. Something equally fun about being a damsel in distress, I guess. Even if it is pretty cheesy.