Sanguine Bond

Enchantment

Whenever you gain life, target opponent loses that much life.

2009-10-01:
Sanguine Bond’s ability triggers just once for each life-gaining event, whether it’s 1 life from Soul Warden or 8 life from Tendrils of Corruption.
2021-03-19:
If an ability triggers whenever an opponent loses life and causes you to gain life, such as the ability of Exquisite Blood, this will loop until either you win the game or a player takes an action to break the loop. If neither of these happen, the game ends in a draw.
2021-03-19:
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, Sanguine Bond’s ability will trigger twice and you may choose a different opponent for each trigger. 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.
2021-03-19:
If you gain an amount of life “for each” of something, that life is gained as one event and Sanguine Bond’s ability triggers only once.