Copper Longlegs

Most proliferate outlets are enters-the-battlefield triggers or repeatable activations that cost nothing but mana; this one asks you to bury the body to fire it. That sacrifice cost is doing real work. A defensive 1/3 with reach that walls fliers early, then converts itself into a single burst of counters once its blocking is spent, folds two jobs into one green two-drop. The choke point is that the proliferate is one-shot: there is no engine here, just a body that becomes a spell when you no longer need the body. That constraint is also what keeps it honest, because a repeatable proliferate on a resilient blocker would have been a different card entirely. What it counts on is a board already carrying counters worth advancing: an extra +1/+1 counter on your creatures, another loyalty on a planeswalker, one more poison, oil, or charge counter across the table. Proliferate adds a single counter of each kind already present, so the payoff scales with breadth rather than depth: the more distinct counters in play, the more that one activation is worth. On an empty board the ability is a dead line, the tell that this was built for a deck already invested in the counter axis rather than one splashing green for a wall. The reach is not incidental filler, either: it lets the card earn its keep in the air on defense during the turns before you cash it in, so the two halves share a timeline instead of competing for one.