Continuity mistake: In "The Gi", Penny drops a journal on the ground and does not pick it up. In a later wide shot, the journal has vanished.
Continuity mistake: The Wattersons are listening to Gumball's conversation through the door, and Nicole is using a drinking glass. In a few shots, Nicole does not have the glass, nor is it on the floor.
The Downer - S3-E37
Continuity mistake: Gumball is being overtaken by the darkness, and there is a coffee table in front of him. When he escapes the darkness in a few shots, the coffee table is missing.
Continuity mistake: Gumball is sitting at the dinner table, and a pile of food is next to his plate. Two shots later, the food disappears.
Continuity mistake: Gumball is on stage at a play. He is saying his line and facing away from the audience. In the next shot, he continues his line, now facing the audience.
Continuity mistake: Toll booth men are throwing fines and tickets at Richard's car. These tickets and fines disappear in a few shots without being blown away by the wind.
Continuity mistake: When Richard is driving down a highway, he makes it into a lane with a truck in it. In two shots, the truck has vanished.
Continuity mistake: Gumball is talking to his dad in front of the couch. In two shots, Gumball is now at the door.
Continuity mistake: Nicole punches the number pad of a telephone receiver, damaging it. Later, Anais picks up the same phone receiver, but the number pad is fixed. No one but Richard touched the phone in the meantime, and he did not fix the phone, either.
Continuity mistake: A man drops a DVD case in the video store. Two shots later reveal an empty store with no DVD case on the ground.
Continuity mistake: Richard's flashback shows him throw money onto the counter. In the next shot, The Money disappears.
Continuity mistake: In "The Spoon", Darwin and Gumball use shopping carts to open the big safe. These carts eventually disappear on their own.
The DVD/The Responsible - S1-E1
Continuity mistake: When they smash the TV something on top falls off. When the camera points back from the little sister, it's gone.
Continuity mistake: Penny sets up a ladder next to Gumball's window. The ladder disappears in the next shot, and reappears in a later shot.
Continuity mistake: After Gumball stops crying, there are still tears on his face. In two shots, the stream of tears disappears.