Doing some testing, I was unable to possess a zombie from the Zombified mod, but that may be more a problem with the other mod than this. But in the Super Block World mod, taking the soul of a goomba with an empty vessel worked fine, but crashed the game when i tried to possess it.

If it helps, the latter involved a portal that seemed to destroy the animal mob body i was occupying.

Thanks for the report ! This looks like an issue in the Super Block World mod though.

crash-2022-01-01_20.58.24-server.txt

May I see the crash report ?