Plague Drone

The 3/3 flyer is the ante; the reason to run this is Rot Fly, which converts every point of an opponent's lifegain into life loss for as long as the demon stays alive. Black has done this work before, but almost always through enchantments: Everlasting Torment and Tainted Remedy install the same "your healing hurts you" lock without a clock attached. Hanging that effect on a creature is the trade the design makes. A body is easier to kill than an enchantment, so the lock is more exposed than the static versions; in exchange you get an evasive attacker that can be flickered, sacrificed, and recur, and that presses damage on its own while the tax runs. The target is transparent. Lifegain props up a wide band of grindy tables, from soul-sisters engines to incidental clerics to lifelink-plus-token loops that float a life total out of burn range, and a static "your gain costs you" turns each of those payoffs into a bleed. That is what separates it from a hatebear that merely switches the faucet off: an opponent who draws into their lifegain plan while this is out is actively losing life, a sharper tax than pure denial. The rate is modest by design, so the card lives or dies on how many life totals it can invert. Against a board with no lifegain it is a plain flyer; against one built on it, it rewrites the whole table's arithmetic.