Learning Curve: Part 1 - S1-E5
Continuity mistake: When the ship has made it through the plasma jump and is approaching the Universal Library, the images of the Watchers the ship passes by go from being transparent, to solid, and then back to transparent.
Buttercrush / Fuzzy Logic - S1-E4
Continuity mistake: When Buttercup punches a hole in the wall to see her sisters are being lowered into lava, the hole's initially quite small. In the next shot, the hole is noticeably bigger.