The Partner ability (CR 702.124) allows a legendary creature with Partner to be paired with another legendary creature that also has Partner — but both cards must have the Partner keyword themselves. You cannot pair a Partner commander with just any commander you choose.
Preconstructed decks that include Partner commanders ship with two specific commanders that both have Partner, chosen by Wizards of the Coast. You are free to swap one or both of those Partner commanders for other legal Partner commanders of your choice when customizing the deck, but each commander you include must independently have the Partner keyword (or a compatible variant like Partner With, which works differently and only pairs with its specific named partner per CR 702.124f).
"Partner With" is a stricter variant: a card with "Partner With [Name]" can only be partnered with that one specific named card, not any other Partner commander (CR 702.124e). So a precon pairing like Gorm the Great and Virtus the Veiled cannot be broken up and mixed with other Partner commanders.
Example: Thrasios, Triton Hero has Partner. You may pair him with Tymna the Weaver (also has Partner) as your two commanders. You could NOT pair him with Atraxa, Praetors' Voice, because Atraxa lacks the Partner keyword entirely.
In summary: Partner commanders in precons are interchangeable only with other generic Partner commanders, and Partner With commanders are locked to their specific named partner.
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.