Belbe, Corrupted Observer
Legendary Creature — Phyrexian Zombie Elf
At the beginning of each player's postcombat main phase, that player adds 
for each of your opponents who lost life this turn. (Damage causes loss of life.)
"Those who wish to become evincar must first cast off the shackles of compassion."
Illustrated by
Commander Legends#270RareEnglishLegality
Rulings
If an opponent lost life and subsequently lost the game, Belbe’s triggered ability still counts that player to determine how much mana to add.
If an effect creates an additional combat phase in a turn, it may also create an additional main phase after that combat phase. Belbe’s ability triggers at the beginning of each of these postcombat main phases.
If an opponent loses life before their own postcombat main phase, Belbe will reward their suffering with mana.