Selvala, Heart of the Wilds is a mythic Legendary Creature — Elf Scout card from Jumpstart (JMP), collector number 429. Current market price: $6.79, TCGplayer market prices via Scryfall.
Whenever another creature enters, its controller may draw a card if its power is greater than each other creature's power. {G}, {T}: Add X mana in any combination of colors, where X is the greatest power among creatures you control.