Loyal Sentry

Mutual assured destruction in a single white one-drop. The trade isn't an upside the card offers in addition to a body; it is the entire transaction. Block anything, and both creatures die regardless of size, which turns a 1/1 into a guaranteed answer to the largest threat on the other side of the board. The design lives entirely on the defensive half of combat: the destruction triggers on blocking, never on attacking, so the Sentry only fires when it stands in front of something. That asymmetry is the discipline that keeps an effect this swingy at one mana. You cannot point it at whatever you like; you have to commit it as a blocker and accept that it dies in the bargain, which prices it well below true removal despite reading like a Maze of Ith with a pulse. It is the deathtouch-style edict-on-a-stick that predates deathtouch being cheap and ubiquitous: the same "size doesn't matter, this creature dies" logic that later got folded into a keyword, here spelled out as a one-shot self-immolating blocker. The wrinkle that earns it a footnote is the symmetry of the kill: because both creatures are destroyed simultaneously, regeneration and indestructible interact in ways most edict effects never have to consider. A small, brittle, perfectly honest piece of early-era combat design.