Which Came First?/Substitute Teacher

Plot:

In "Which Came First?", when a field trip across the desert is ruined by the school bus' flat tire, Billy, Mandy and Grim go into a cave infested by giant mutant chickens. In "Substitute Teacher", Nergal Junior's first day at his cousin Billy's school results in him being bullied by Sperg, so he transforms into Ms. Butterbean, the school teacher, to exact revenge.