Continuity mistake: When Gumball and Darwin board the bus, the bus driver pulls out an axe and the boys ask what it's for. The driver says he uses it to push the pedals and he is still holding it. In two shots, the axe has vanished.
Other mistake: Nicole is through a window of the house in the scene when Darwin asked "Which one is the real Gumball?" This is probably from the episode "The Goons." (00:00:05)