Greenbelt Guardian

A repeatable trample donation is the kind of green filler that fills out a curve without asking for a second look; the once-ever pump is what makes this Elf worth the slot. Three +1/+1 counters for four mana turns the 2/2 into a 5/5, but the game will only ever let that happen once, so there is no runaway threat to plan around and no reason to hold mana up early waiting for a better window. That single-use restriction is what pays for the generous rate: an ability you could fire every turn would have to be priced defensively, while a one-shot line can hand you three counters at a discount because it can never snowball. The two abilities dovetail once you see the plan. The counters make the body worth swinging with; the cheap trample lets those counters push damage through a chump blocker, whether you donate the trample to this creature or to a bigger threat elsewhere on the board. It is a design organized around a decision that surfaces exactly one time per game, which is precisely what the exhaust keyword exists to enable: a card can carry a powerful line without carrying the balance headaches that repeatable power usually brings.