Emperor's Vanguard is a rare Creature — Human Scout card from Ixalan (XLN), collector number 189. Current market price: $0.17 (foil $0.25), TCGplayer market prices via Scryfall.
Whenever this creature deals combat damage to a player, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)