Weirdmageddon: Part 1 - S2-E18
Continuity mistake: Two guys are throwing a frisbee and it lands on the ground. In the next shot, the frisbee is gone.
The Hand That Rocks the Mabel - S1-E4
Continuity mistake: When Mabel gets back from her date with Gideon, she finds Dipper reading the 3rd journal on the sofa. However, there is a 2 on the book instead of a 3. (00:06:08)
Weirdmageddon 2: Escape from Reality - S2-E19
Continuity mistake: Mabel uses a needle to burst out of Mabeland. The needle disappears in the next shot.
Weirdmageddon 2: Escape from Reality - S2-E19
Continuity mistake: Craz drops a microphone, which disappears by itself in a few shots.
Weirdmageddon 2: Escape from Reality - S2-E19
Continuity mistake: Bill is holding a spoon, but when the camera cuts away and back, he is not holding the spoon anymore. This also happens to Ford when holding him.
Weirdmageddon: Part 1 - S2-E18
Continuity mistake: Grunkle Stan drops a hammer after a goat pulls on him. In two shots, the hammer on the ground disappears.