Sadistic Obsession

This is a repeatable removal factory dressed as an Aura, and the interesting part is where the removal actually lives. The kill ability sits on the enchanted creature, not on the Aura or its controller, which means the recurring source of -1/-1 counters is any body you glue this onto: an evasive attacker, a mana dork that would otherwise tap for nothing on defense, a creature you already expect to stick around. Each activation costs a black mana and taps the host, so the drain on your board is real; you are trading the enchanted creature's attention every turn for a permanent point of shrink somewhere else. Because the counters are -1/-1 counters rather than a damage or -X/-X effect, they stack across turns and grind down anything without a bump, and they close the gap on indestructible or damage-immune threats that ordinary burn cannot touch. It also plays as attrition on your own side when you want it to: a slow, sanctioned way to feed counters onto creatures for whatever cares about them, or to euthanize a creature you would rather sacrifice for value. The rationing is what keeps the open-ended effect honest: strong as the ability is, it costs a body and a tap every turn, so the plan only works when you can spare one creature for removal duty instead of the full attack.