Inti, Seneschal of the Sun is a rare Legendary Creature — Human Knight card from The Lost Caverns of Ixalan Promos (PLCI), collector number 156p. Current market price: $2.01 (foil $2.29), TCGplayer market prices via Scryfall.
Whenever you attack, you may discard a card. When you do, put a +1/+1 counter on target attacking creature. It gains trample until end of turn. Whenever you discard one or more cards, exile the top card of your library. You may play that card until your next end step.