Ordeal of Heliod is a uncommon Enchantment — Aura card from Masters 25 (A25), collector number 27. Current market price: $0.13 (foil $0.50), TCGplayer market prices via Scryfall.
Enchant creature Whenever enchanted creature attacks, put a +1/+1 counter on it. Then if it has three or more +1/+1 counters on it, sacrifice this Aura. When you sacrifice this Aura, you gain 10 life.