Will-o'-the-Wisp is a uncommon Creature — Spirit card from The List (PLST), collector number A25-115. Current market price: $0.26, TCGplayer market prices via Scryfall.
Flying (This creature can't be blocked except by creatures with flying or reach.) {B}: Regenerate this creature. (The next time this creature would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)