Answer: Artie
When Shrek was first arrested, he said some pretty mean things to Artie in order to protect him from the guards. Artie believed Shrek and left, angry and dejected. Donkey and Puss convinced him that Shrek had only been looking out for him.
So Artie returns in the middle of the onstage fighting and calls everyone to stop. He gives a stirring version of the speech that Shrek had given to him, about being who you knew you could be, and not who other people expected you to be. The fairy tale creatures, who have been working with Charming, take Artie's words to heart and abandon the fight, leaving Charming without his army.