Grim Poppet

The 4/4 in the P/T box is a fiction the moment it resolves: three -1/-1 counters knock the body down to a 1/1 before it can do anything. Those counters are not a tax, though, they are the ammunition, and the way they discharge runs the same logic in both directions. Each counter you remove puts a permanent -1/-1 counter on another creature while growing the Poppet a point closer to its printed body, so firing the engine softens the board and rebuilds your own threat at once. You get three guaranteed counters to distribute: scattered across blockers to shave a board, or stacked onto a single target to drop a three-toughness creature outright. The counters it deals stick on whatever they land on, so a point chipped off a creature stays chipped even as the next turn comes around. But the engine is strictly finite, because the activation spends a counter rather than firing for free: once the Poppet has burned through all three and grown back to its 4/4, the toolbox is empty, the body is a slow beater whose ability lies dormant until it gets more counters. Pair it with a source that adds fresh -1/-1 counters, or a proliferate effect while a counter still remains, and the one-shot becomes recurring. Among the colorless wither-flavored designs of its era, this is the one that packaged the mechanic into a portable removal toolbox, with the body's own decay paying the entry fee.