Death's-Head Buzzard

Dying is the activation here, not a downside. The death trigger turns this Bird into a board-control trade that punishes anyone who killed it: block it, burn it, or feed it to a sacrifice outlet, and every other creature shrinks by a point of toughness at once. That makes it most dangerous in a board state full of tokens and one-toughness utility creatures, where a single death sweeps the field clean while the controller's larger bodies survive. The cost of admission is the fragile 2/1 frame, which means the effect is rarely free: it wants to attack into a profitable block, or it wants a sacrifice engine to pull the trigger on command rather than waiting for an opponent to oblige. The symmetry of the wipe is real (your own small creatures die too), so the build that wants this is one that runs few one-toughness creatures of its own or simply welcomes the trade. It belongs to the small family of creatures whose death is a deliberate board action, alongside effects that punish removal by leaving a mess on the way out, and the flying body gives it just enough evasion to force the unfavorable block that springs the trap.