Captain Underpants and the Preposterous Pulverizing of the Pestering Poopacabra

Captain Underpants and the Preposterous Pulverizing of the Pestering Poopacabra

Available on Netflix
S2 E4: George and Harold train a rat in hopes of getting extra credit. However, it soon escapes into the sewers and gets covered in toxic waste, turning it into Poopacabra.