I'm Cameron Williams, a card designer on Magic: The Gathering FINAL FANTASY and Studio X's very own FINAL FANTASY XIV fanatic
While controlling an opponent, you can't make any choices or decisions for that player related to tournament rules
And that, my friends, is the power of a well-chosen sideboard card
Urza, Lord High Artificer [Best Commander for Artifact-Based Decks] Every artifact you control taps for blue mana the moment Urza enters
Terror of the Peaks We just got the ugliest version possible in a Secret Lair, so that might be the cheapest play here
Normally, neither player receives priority during the cleanup step, so nobody can cast spells or activate abilities