Wildcall is a rare Sorcery card from Ugin's Fate (UGIN), collector number 146. Current market price: $1.00, TCGplayer market prices via Scryfall.
Manifest the top card of your library, then put X +1/+1 counters on it. (To manifest a card, put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)