Revealing mistake: In the song "Living Island", we see Judy frog jumping over Pufnstuf. When she goes back down, the wires holding her up and putting her down are visible.
H.R. Pufnstuf (1969)
1 revealing mistake in show generally - chronological order
Starring: Billie Hayes, Joan Gerber, Jack Wild, Lennie Weinrib
Revealing mistake: When Cling and Clang hit Witchiepoo and see flies in the air and falls, the wire lifting her up is visible.
Witchiepoo: With friends like you two, who needs enemies?