Watcher of the Wayside is a common Artifact Creature — Golem card from Tarkir: Dragonstorm (TDM), collector number 249. Current market price: $0.18 (foil $0.23), TCGplayer market prices via Scryfall.
When this creature enters, target player mills two cards. You gain 2 life. (To mill two cards, a player puts the top two cards of their library into their graveyard.)