Tainted Strike

Poison wins at ten, not twenty, and this is the cheapest way to graft that fact onto a creature that was never built to abuse it. For a single black mana at instant speed, the entire damage figure of one body converts into poison counters for the turn, so a threat the defending player had budgeted against on a twenty-point life scale suddenly counts against ten. The +1/+0 is almost incidental: the real gift is the infect grant, and it does its work after blocks are declared, when the opponent has already committed to a math that no longer applies. That makes it a combo enabler rather than a fair combat trick. It cares about exactly one thing: how much damage you can stack onto a single creature. Hand it to anything with trample or evasion, multiply that lump with pumps, and a comfortable life total becomes a dead one in one swing. The danger isn't the rate, it's the conversion. A creature that read as a chip-damage nuisance becomes lethal the instant this resolves, and the opponent rarely catches the counting error until the poison counters are sitting on the table in front of them.