Ob Nixilis, Captive Kingpin

The trigger is the design's whole argument: not "whenever an opponent loses life," but whenever one or more opponents each lose exactly 1 life. That one word does the balancing. It shuts out the big burn spell and the fat combat hit; a single point is the currency, so the card wants a stream of pingers, drainers, and incidental one-life leaks rather than one large swing. Each satisfied trigger does two things at once, growing the body with a +1/+1 counter and turning that pinprick into a card off the top you can play until your next end step. That second clause is the greedier one: a demon that converts a diet of small drains into raw card advantage, then flies over on an ever-larger frame with trample to close. Note the ceiling built into the condition, though: "one or more opponents" means a single effect that clips several players for one apiece still only fires the ability once, so the reward comes from frequency across turns, not from how many people you tag at the same moment. What keeps it from being oppressive is the fragility underneath the value: a 4/3 that has to survive to compound, and a trigger specific enough that a deck built on raw damage never switches it on at all. This is a demon that rewards bleeding a board by inches, not hammering one player flat.