Oni Possession

The +3/+3 and trample come first; the upkeep tax arrives like the bill afterward. That recurring sacrifice is the whole bargain: keep the buff alive and the Aura eats a creature on each of your upkeeps, so the math only works if you have a stream of expendable bodies to feed it, or you intend to win before the loop catches up. The Demon Spirit type change is mostly flavor, a nod to the host being hollowed out and inhabited, though tribal payoffs can read it either way. What makes the card a curiosity rather than a beater is the upkeep timing: the sacrifice happens on your turn, not when the Aura enters, so a freshly cast Oni Possession buys you a swing before the demand comes due, and you can always sacrifice the enchanted creature itself to dodge the obligation, which dumps the Aura along with it. It is a fragile, demanding kind of pump, the sort of self-cannibalizing enchantment from an era when black's beefiest effects were priced with a recurring cost attached rather than a one-time downside. The deck that wants it is one already manufacturing tokens or chaff faster than it can lose them, where the tax becomes a feature: a sacrifice outlet bolted onto a trampler.