When Brinelin enters and whenever you cast a spell with mana value 6 or greater, you may return target nonland permanent to its owner's hand.
Partner (You can have two commanders if both have partner.)
Brinelin is a mono-blue control/big-spells deck that uses expensive spells to repeatedly bounce threats, blockers, and problem permanents. You ramp into 6+ mana value bombs, generate value off every cast, and grind the table down before closing with a haymaker or large evasive threat. Partner lets you pair Brinelin with another partner commander for added flexibility.
Repeatable, flexible removal that hits any nonland permanent including commanders and protected threats
Mono-blue access to the best counterspells, card draw, and ramp rocks
Each big-mana spell becomes two-for-one value, smoothing out tempo
Partner ability adds deckbuilding flexibility and an extra command-zone body
Eight mana is a steep cost and Brinelin dies easily to removal once on board
Bounce only delays permanents rather than permanently answering them
Mono-blue struggles with enchantments and answering resolved problems beyond tempo
High curve makes you vulnerable to fast aggro and stax before you stabilize
Steals multiple permanents while satisfying Brinelin's cast trigger for extra value.
Lower your curve's clunkiness by adding efficient ramp (Sol Ring, mana rocks, High Tide) and the strongest blue interaction (Force of Negation, Mana Drain, Fierce Guardianship) so you reliably hit 6+ MV spells while protecting Brinelin. Add blink and untap enablers like Thassa, Deep-Dwelling and Ghostly Flicker to abuse the enter trigger, and lean into a tight win package such as Cyclonic Rift overload into a beatdown or an infinite-mana High Tide loop. Choosing a strong partner can expand your answers and add a more reliable closing combo.