Chumbanotz
commented
3 years ago I've seen this happen before, although I've had trouble recreating it for testing. This issue existed in the original Mutant Creatures mod as well. I think I've found a way to fix this. If this happens to you, you can either leave and reenter the chunk the mutant zombie is in, or reload the world. One way to prevent this is to set the mutant zombie on fire right before it dies.
The mutant zombies in my world consistently, if I don't get to them in a timely manner with a flint and steel, it fades away but returns invisible & only and only able to be damaged by environmental hazards.
However if another player teleports to the player now running away from the invisible mutant Zombie, they can fight it normally and see it