Regeneration is a common Enchantment — Aura card from Mirage (MIR), collector number 236. Current market price: $0.13, TCGplayer market prices via Scryfall.
Enchant creature (Target a creature as you cast this. This card enters attached to that creature.) {G}: Regenerate enchanted creature. (The next time that creature would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)