Reincarnated other beings

Do angels elementals demons priests/priestesses aliens incarnate as humans?with definite missions?

Anything can incarnate as a human given the circumstances are right. But as always with incarnations you have to start again from scratch each Time because human bodies have limitations that have to be overcome by will. Even the Dali Lama only remembers bits and pieces and he is the foremost expert on maintaining memmory through incarnations. There are many reasons something might incarnate not just for some mission but it’s fun to eat, have sex, and do drugs and alchohol and this is one of the few places to do it.