Ochre Jelly
The iconic dungeon slime rendered as a mechanical toll: kill it and it does not simply die, it leaves behind a smaller copy of itself. The Split ability turns one scaling body into a chain of diminishing successors, each entering with half the previous count rounded down, so an X of six leaves a six-counter Ooze that becomes a three-counter token that becomes a one-counter token before the line finally runs out (one counter is not two, so the last copy dies for good). That halving is the governor on what would otherwise be a recursion engine you could never profitably block: every death costs the survivor half its mass, so the value is finite and front-loaded rather than open-ended. It rewards being cast large, because you need two or more counters for the split to fire at all, which quietly punishes the small early plays that make most X-creatures forgettable. Trample matters more here than on a typical fatty, since the counters translate directly into unblocked damage and even a single shrunken successor keeps pressuring. The real texture is in the timing: the copy arrives "at the beginning of the next end step," so it appears after combat and after most sacrifice loops have resolved, dodging the cleanest answers. Note the flip side of that dependence on X, though: it is a 0/0 whose entire body comes from the counters it enters with, so any effect that returns it to the battlefield brings it back with none, and it dies on the spot.
