Belbe, Corrupted Observer

• WWizards of the Coast2020-11-10
  Official Ruling
  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.
• WWizards of the Coast2020-11-10
  Official Ruling
  If an opponent loses life before their own postcombat main phase, Belbe will reward their suffering with mana.
• WWizards of the Coast2020-11-10
  Official Ruling
  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.

Rulings via Scryfall