A-Skyclave Shadowcat

The Alchemy rebalance (the A- prefix marks a card retuned for Arena, distinct from its paper printing) turns a plain sacrifice creature into a self-referential aristocrats engine. The elegance is that both halves key off the same resource pointed two directions. Pay black and eat one of your own creatures, and the Shadowcat grows; every counter you spend a body to add is also arming this Cat as an eventual cantrip, because the second ability fires when any creature you control bearing a +1/+1 counter dies. The Shadowcat can only counter itself up, so the loop points inward by construction: you are building a growing threat that refunds a card the moment it finally dies, whether you feed it to your own outlet or lose it in combat. Where the sacrifice-for-value creatures it descends from buy one effect per body and stop, this one asks a single black mana per activation to do two jobs at once: it trims a creature off your board into a bigger Cat, and it sets up a refill on the back end, both through one +1/+1 counter doing double duty. The activation cost never changes (you still need black mana and another creature to sacrifice every time), so this is not a self-accelerating loop; it is a slow-grind engine where the counter is simultaneously the payment record and the death-trigger condition, and that overlap is the whole design.