Bird and I's neosonas, finally working out this concept, or starting to...!
He's the little Bloop blob, a petpet.
Mine is the Christmas Zafara.

the petpet has a very crude possession ability... though her lower half remains under some of her own control, and in high emotions [such as panic or distress], she can manage entire motions like kicking her legs, running, swatting her tail around, etc. He is capable of puppeting her entire body, but it's easier if she offers no resistance. He only has enough mass to cover just her head and arms, but the head is most important-- he has some degree of control over her brain, so he can force movements.. sometimes he enjoys controlling the whole thing, other times he likes leaving her control of the lower half. If he relaxed, she could still control the black arms and head. He could reduce himself to only a benign coating, or he can exert complete control. I imagine he's very whimsical and fickle about it, alternating to the point of it being disorienting.

Still much to think about and work out...! I'm not sure if I want the blackened form to still have her ears, or only the horns. And I'm still workshopping their overall dynamic, why it's this way.. for once I want to start with an indulgent aesthetic concept and work backwards from there!