I had a L2 sovereign beat a Dark Wizard once on autoplay.  No idea how it happened, and I also wish I had looked at the details.

I took on a dark wizard with 2 ritualists and an assassin demon with him using two L14 champs. I had an unlucky start to the battle and didn't kill any of them except doing some damage to the demon. So, the dark wizard got off his despair bomb. It killed the champ with the lower HP and brought my other one down to 1 HP. I then went rage autocalc at my "bad luck", and somehow the autoplay screen showed my 1 HP champ as the victor... Once again, I forgot to check details. I guess I was in shock.

Anyways the point is the autoplay can yield some insane results.

Yeah autoplay often has some pretty silly results happen. It's quite often that I've pressed it to end a combat I know is an entirely lost cause, and it decides I won. Not just won, but won pretty crushingly. That's how I beat Abeix the first time I ever faced him. I went in with a load of spearmen, thought I was doing ok until he stopped spitting and bothered to hit me, and I ended up clicking the autoplay when it was clear he was going to three-hit kill splash damage all my men. Oh, I won. Right. Whatever...

It's at the point where I'm learning what combats can be 'cheesed' for an unrealistic autoplay result instead of carrying it out myself. Night Widows at the start of the game for example; my sovereigns are guaranteed to kill them with no return damage. Or Bear Cubs, which will maul the shit out of you in combat at the start of the game, but autoplay vastly reduces their damage potential to something fairly predictable.