Revealing mistake: When "Krebbs" the koala is discussing with his other friends in the cell. If you look closely, you can notice a blink in the outline in the "Krebbs" nose. It's a clear ink & paint mistake of the blur line.
Revealing mistake: When Webby and the others are standing outside of the window watching Scrooge pace back and forth in anger, she casts no shadow on the patio. This is revealed when she moves left at one point. (00:28:50)