I want to be able to project my spirit into animals and possess them. If this had to be limited to one group in particular, I'd choose arthropods (though that's a pretty huge group). My human body could lie around and sleep while I flew around as a moth or hunted as a spider, and I could use it for getting trapped or pest insects out safely for both of us. Or I could indulge myself and possess a wasp, which would conveniently sting people I dislike. Expanding on this I could probably possess any number of spiders and become an untraceable assassin, but... Neh. Anyway, there'd probably be a range limit.