S1·E27 No More Mr. Nice Guy

To help Mon-Star, Yess-Man joins him in the Transformation chamber but, the effects of the Moonstar of Limbo have an adverse affect on Yess-Man's personality as he tries to take over the Mob. After, Mon-Star takes care of the bandits trying to start a rival mob, Timestopper comes and lets Mon-Star know what's going on. Mon-Star promptly goes and confronts Yess-Man and puts him back in his proper place.