Selvala, Eager Trailblazer is a mythic Legendary Creature — Elf Scout card from Outlaws of Thunder Junction Promos (POTJ), collector number 231p. Current market price: $0.52 (foil $0.58), TCGplayer market prices via Scryfall.
Vigilance Whenever you cast a creature spell, create a 1/1 red Mercenary creature token with "{T}: Target creature you control gets +1/+0 until end of turn. Activate only as a sorcery." {T}: Choose a color. Add one mana of that color for each different power among creatures you control.