Adder-Staff Boggart is a common Creature — Goblin Warrior card from Lorwyn (LRW), collector number 148. Current market price: $0.18 (foil $0.39), TCGplayer market prices via Scryfall.
When this creature enters, clash with an opponent. If you win, put a +1/+1 counter on this creature. (Each clashing player reveals the top card of their library, then puts that card on their choice of the top or bottom. A player wins if their card had a greater mana value.)