Phyrexian Reaper

Color-pie hate, drawn as a knife that only cuts one way. Black's longstanding feud with green gets a literal expression here: a body that becomes a death sentence the moment a green creature steps in front of it, with regeneration shut off so the standard green escape hatch is closed too. The wrinkle is that the ability triggers on being blocked, not on blocking, so the green player has to choose between eating the damage and feeding a creature to the void; the defender pays for the crime of stepping in. This is anti-color combat tech of an older school, where the punishment was wired directly into the attack step rather than imposed from across the table by a tax or a static effect. Against any other color the trigger simply never fires, leaving a plain attacker, and that narrow window is the bargain: the cost only justifies itself if the opponent is leaning on green chump-blockers to survive, at which point the creature reads less like a threat and more like a levy on green's defensive plan. It is a museum piece of an era when sets shipped color-versus-color grudges as printed cardboard rather than abstracting them into keywords, and the flavor of a Phyrexian butchering its way through green growth does most of the heavy lifting the body cannot.