In the episode "The Eye of the Beholder", during the scene in which the kids are walking through the Mushroom Forest, where they get attacked by slug/snail-like creatures. From exactly 7 minutes and 18 seconds, 'til 7 mins 20 secs, the lower parts of Presto and Diana are missing!

You'll notice the line to where the cut-off point is on the cel, marking the end of the image area.