Taking the most powerful character and writing them out of the story or arc, to preserve the drama and make things tougher for the main cast.
So you've got a villain running amok, and a designated plucky underdog hero who's been set up to save the day.
Looks like time for some heroic derring-do, but wait — there's a supporting character who's way, way, Well, obviously we can't have that, and if the character in question is any kind of good guy it would strain belief to have them just sit out the fight for no reason.
Sure, you could kill them off or write them out of the story completely, but they don't have to leave , just long enough for the hero to have to face the menace du jour on his or her own.
The solution: take the bruiser and put them on a bus for a while.
Maybe some other responsibility came up, maybe there's another villain rampaging around somewhere else, maybe they had the bad luck to break a leg and got stuck in the hospital, maybe they were arrested and are showing Self-Restraint.
However it's done, the Deus ex Machina is temporarily out of commission, and the weaker heroes have to win the fight on their own.
If the villain is smart enough, they will find a way to invoke this by luring the character out of the way before setting the plan in motion, but the character can come off as rather feeble-minded if they were easily called away by some paper-thin ruse, leaving in jeopardy whatever the villain was after.
Alternatively, this may come into play when the main hero is much more powerful than the supporting cast; in order to give them A Day in the Limelight, the all-powerful hero needs to be depowered, incapacitated, or distracted.
An alternative approach is to have an immensely powerful character actually join the plucky underdog's team for the big epic battle. Any given Deus Exit Machina may or may not end with the character returning in the nick of time to save the day.
He could easily save the day with a snap of his fingers..then that character is immediately knocked out or otherwise disabled so that the story can actually be interesting. If it's a Stealth Hi/Bye then you have a simple case of Villain Teleportation by a Mobile Menace. An especially common way to deal with Reality Warpers or Loads and Loads of Characters (especially if they Can't Catch Up).
(This can also have the side effect of making the villain that much more threatening.) On rare occasions, it may be a villain far higher up the Sorting Algorithm of Evil who drops by for a Final Boss Preview to foreshadow the difficulty of future encounters before giving the weaker villain back his Worf Effect. Holding Back the Phlebotinum is a Sister Trope which is about powers/weapons/Mac Guffins instead of the characters themselves.