Whenever Bruse Tarl enters or attacks, target creature you control gains double strike and lifelink until end of turn.
Partner (You can have two commanders if both have partner.)
Bruse Tarl turns one big creature into a one-shot kill machine, granting double strike and lifelink every time he enters or attacks. Build a Voltron shell that suits up a single attacker, swing for lethal commander damage, and use the lifelink buffer to stabilize while you set up. Partner lets you splash a third or fourth color of support by pairing him with another partner legend.
Repeatable double strike effectively doubles your best attacker's power and combat triggers
Lifelink gain stabilizes you against aggro and racing strategies
Partner gives huge deckbuilding flexibility and access to a second command-zone threat
Cheap to recast at four mana, keeping the trigger online after removal
Doubles damage from trample/infect/poison and any 'when this deals combat damage' payoffs
Only buffs one creature, so single-target removal or blockers shut down your turn
Bruse himself has no evasion and a small body, making his attack trigger easy to chump
Reliant on having a quality creature already in play to target
Vulnerable to board wipes that erase your invested Voltron threat
Boros/RW lacks strong card advantage and ramp without going wide
Anthem-style double strike for your whole team to push a go-wide finish.
Tighten the curve with premium evasion equipment (Sword suite, Lightning Greaves, Whispersilk Cloak) and protection like Swiftfoot Boots and Heroic Intervention to keep your threat alive. Choose a partner that patches Boros weaknesses—Tymna the Weaver for card draw, Kraum for cards and evasion, or Rograkh for cheap combo enablers—and add fast mana like Sol Ring, Fellwar Stone, and Smothering Tithe. Finish with redundant double-strike and overrun effects so the deck still wins after a wipe.