Light of Promise

Enchantment — Aura

Enchant creature
Enchanted creature has "Whenever you gain life, put that many +1/+1 counters on this creature."

2020-06-23:
If 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.
2020-06-23:
Each 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.
2020-06-23:
If you gain an amount of life “for each” of something, that life is gained as one event and the ability triggers only once.
2020-06-23:
In 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.