Sentinel Totem is a uncommon Artifact card from Ixalan (XLN), collector number 245. Current market price: $0.20 (foil $0.51), TCGplayer market prices via Scryfall.
When this artifact enters, scry 1. (Look at the top card of your library. You may put that card on the bottom.) {T}, Exile this artifact: Exile all graveyards.