Testing old work on new update, saw a floating creeper head. (Pic 1)
Started a new world on localhost server...
Spawned some creepers, all invisible. (Pic 2)
Tested with other mobs, Affects Creeper, Witch, and Squid. (Pic 3)
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Creepers are invisible but show a creeper head skull instead.
I can reproduce this glitch.
Witches and squids are also invisible, they do not have a visible skull though.
I forced a crash, posted log.