The Odyssey - S1-E14
Continuity mistake: When Wilson jams the pistol in Oliver's face, Wilson is holding the gun in his right hand. When the shot changes, it flips - he is suddenly holding it in his left hand, and his previous un-scarred left eye now has some scrapes around it.
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)