I Know All, I See All

Since your opponents take a shared team turn, they all have the same untap step. Your permanents untap just once during that step, no matter how many opponents you have.

As an opponent’s untap step begins, if you control this face-up scheme card, all your permanents untap during that untap step. You have no choice about what untaps. Those permanents untap at the same time as the active players’ permanents.

During an opponent’s untap step, effects that would otherwise cause your permanents to stay tapped don’t apply because they apply only during *your* untap step. For example, if you control a Deep-Slumber Titan (a creature that says “Deep-Slumber Titan doesn’t untap during your untap step”), you untap Deep-Slumber Titan during each opponent’s untap step.