Cheapest priced copy (Core Set 2021): $0.99 at Card Kingdom, near mint, their price list as of .
Light of Promise 
Enchantment — Aura · Uncommon · Core Set 2021 · #25
Enchant creature
Enchanted creature has "Whenever you gain life, put that many +1/+1 counters on this creature."
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.99 to $2.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Core Set 2021 | 25 | Uncommon | $0.99 | $2.49Out of stock |
| Marvel Universe | 46 | Mythic | $1.29 | $2.99 |
4 rulings from Wizards of the Coast
- 23 June 2020If you gain an amount of life “for each” of something, that life is gained as one event and the ability triggers only once.
- 23 June 2020In a Two-Headed Giant game, life gained by your teammate won't cause the ability to trigger, even though it caused your team's life total to increase.
- 23 June 2020If enchanted creature is dealt lethal damage at the same time that you gain life, it won't receive a counter from its ability in time to save it.
- 23 June 2020Each creature with lifelink dealing combat damage causes a separate life-gaining event. For example, if two creatures you control with lifelink deal combat damage at the same time, the ability will trigger twice. However, if a single creature you control with lifelink deals combat damage to multiple creatures, players, and/or planeswalkers at the same time (perhaps because it has trample or was blocked by more than one creature), the ability will trigger only once.