Note the mana value of each card as it's put into exile.
Bell Borca's power is equal to the greatest number noted for it this turn.
At the beginning of your upkeep, exile the top card of your library. You may play that card this turn.
Bell Borca turns every exile event into a stat boost while providing card advantage via upkeep impulse draw. You play a midrange-to-spellslinger game in Boros, exiling high-mana-value cards to swing for huge combat damage or pivot into a goad/attack-trigger commander damage plan. Each turn you advantage off the free upkeep card and pump Bell with big spells or exile effects.
Reliable card advantage every upkeep with the impulse draw, smoothing draws and enabling tempo
Cheap commander that can become enormous, threatening fast commander damage out of nowhere
Synergizes with exile-matters effects (impulse draw, foretell, suspend) and big-mana-value spells
Boros gets great equipment, extra-combat, and damage-doubling support
Power is recalculated each turn and resets, so it's inconsistent without setting up exiles
Vulnerable to removal and chump blocks like any Voltron-leaning creature
Boros traditionally lacks ramp and card-engine depth outside the commander
Decks can be parasitic—needs to actively engineer high-MV exiles to stay big
Haste lets Bell attack immediately and capitalize on exile pumps the turn they happen.
Add evasion and protection (Whispersilk Cloak, Swiftfoot Boots, Sunforger package) so Bell connects reliably, plus damage doublers like Gratuitous Violence and extra-combat enablers. Lean into consistent high-mana-value exiles via Bonus Round, foretell, and cascade/Etali effects to guarantee a big Bell every turn. Shore up Boros's weaknesses with rocks (Arcane Signet, Smothering Tithe) and card filtering so the upkeep impulse stays relevant.