The End of Flutter Valley (1) - S1-E1
Corrected entry: As the witches' spell begins the Ponies pause and look around. Sundance (white Pony with pink hair) is standing with the group, yet she does not feature at all in this set of episodes.
The Golden Horseshoes (1) - S2-E6
Continuity mistake: As Sweet Stuff is talking to Surprise near the beginning of the episode, both of their legs are drawn far too short, making them look deformed.
Correction: There are lots of movies that show characters that are not primary to the plot line, much like an extra.