It's a simple thing, you see. Just to take over a body, humans that is. Demons are extremely hard to take over. And angels? Those damn beasts! They have so much power but do not share it. If you are a spirit you may find some humans, the ones with a sixth sense, rather difficult to take over. They are aware of your presence and will most likely try to stop you. This is not true for all spirits of course some are much stronger than others.
Demons can actually take over any human with ease. (Aren't we awesome? mrgreen ) And Angels. Pfft! Don't get me started. They can take over anyone even us Demons. They even have the guile to kick us out of humans that we've already possessed! Damn beasts!! I'll show you! I'll take one of YOU over! See how you like it!
~Last words of Dracon of Rathfeild. Missing since the year of wrathful plans.~