Will-o'-the-Wisp is a rare Creature — Spirit card from Revised Edition (3ED), collector number 137. Current market price: $5.15, 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.)