Culvert Ambusher is a uncommon Creature — Wurm Horror card from Murders at Karlov Manor (MKM), collector number 158. Current market price: $0.13 (foil $0.17), TCGplayer market prices via Scryfall.
When this creature enters or is turned face up, target creature blocks this turn if able. Disguise {4}{G} (You may cast this card face down for {3} as a 2/2 creature with ward {2}. Turn it face up any time for its disguise cost.)