Venomous Breath

Mark a creature, and every creature that fights it this turn is condemned: the destruction doesn't resolve on damage, it waits for end of combat and then sweeps everything that blocked or was blocked by your chosen target. That delayed-trigger structure is the whole reason this plays differently from a deathtouch creature. The marked attacker or blocker can die in combat damage and the destruction still fires, dragging down every creature that touched it, your own included if you chose poorly. It turns a single body into mandatory, total bait: green's answer, in an era before the color had clean removal, to a board clogged with too many blockers. Make blocking itself lethal and the math of attacking into a wall changes, but only on your terms, and only when the opponent steps in. The cost is the tell. Four mana at instant speed for something that does nothing unless combat actually happens means it sits inert on stalled turns or whenever your opponent declines the fight. This is slow, conditional, contingent removal that needs the opponent's cooperation to do its job, which is exactly the shape of green's combat answers from this period: punish the engagement rather than prevent it.