At the beginning of each postcombat main phase, the active player adds for each of your opponents who lost life this turn. (Damage causes loss of life.)
Belbe turns combat and pinging into a colorless mana engine: whenever your opponents lose life on your turn, you flood your postcombat main with per damaged opponent. Spread early aggression or repeatable damage, then dump the extra mana into big payoffs, X-spells, and reanimation. You win by snowballing a mana advantage into oversized threats and combos faster than the table can answer.
Ramps explosively in multiplayer—hitting three opponents adds six colorless on your turn
Cheap two-mana commander that comes down early and stays relevant all game
Rewards aristocrats, aggro, and ping effects you'd run anyway
Colorless mana fuels Eldrazi, X-spells, and big artifacts without color strain
Mana only appears in postcombat main, so you must plan to actually spend it
Provides no protection or evasion for itself—easily chump-blocked or removed
Generates mana for the active player, so it can help opponents on their turns if they damage each other
Needs reliable repeatable damage sources to be consistent, not just a one-time hit
Drains the table and converts surplus colorless mana directly into a win.
Add fast mana (Dark Ritual, Sol Ring, mana dawn artifacts) and cheap repeatable pingers so Belbe triggers every turn, then lean into a dedicated mana sink package like Torment of Hailfire, Comet Storm, or Eldrazi titans. Tutors (Demonic Tutor, Diabolic Intent) find your damage engine, and protecting Belbe or pivoting to commander-independent damage sources keeps the engine online. For higher power, build toward aristocrats loops (Blood Artist plus sacrifice fodder) that simultaneously drain opponents and refuel your colorless ramp.