So my character was introduced by having gotten in the way of a certain noble and being chased by the guards, and that's when she met the party. Later on, one of our players would trip over the gnome, a discussion would ensue, spells would be traded, and we'd quickly find out she was not an ordinary caster; one of the players tried to put her into a Bag of Holding and she plane shifted out of it. We run away, guards are called, we fight. The players scatter after the fight, stealthing their way to a meet up point. There was only one problem; our half orc, Demetrius, had joined late, and, hungry for a battle, he went back to where we fought the guards. Alone. And the Wizard was there.

Keep in mind, none of us had that big of an attachment to Demetrius yet, so if he was arrested there, none of us would rescue him. We all thought this was it, Demetrius' end. However, since he had just joined, he didn't know much what was going on, so we roleplayed it out as if he was distracted and spaced out. The Wizard cast Hold Person, DC 18. Demetrius fails the first check, but succeeds the second one with a flat natural 20. "Don't worry, little lady, I'll save you from those evil guards!" He said. The Wizard cast Submission. Demetrius rolls another nat 20. He picks up the powerful gnome and runs from the guards. They are too dumbfounded and confused to move.

The wizard could not use somatic components while grappled, and had lost a lot of spell slots. She had one thing left. Wish. And with her d100, she rolled a 1. Demetrius triumphantly carried the defeated mage to the meeting point, lifted her up like Simba in the Lion King. "I've saved you, child!". We managed to take the diplomatic approach and convince her to get the guards to stop looking for us, as well as give the captain of our ship a promotion in exchange for being let go.

So yeah, Demetrius defeated singlehandedly a level 20 wizard, countering her large intelligence with equal stupidity.