The Stand-in - S1-E9
Revealing mistake: When Pufnstuf tries to reason with Witchiepoo, Witchiepoo hits him with a giant powder thing and shouts "Make up." When Pufnstuf falls over his head almost disconnects to his body.
H.R. Pufnstuf (1969)
1 revealing mistake in The Stand-in
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: Stop eating your popcorn and be quiet.