Revealing mistake: It's obvious the 3 blind witches have cloths covering their eyes.
Suggested correction: Yes, they do, but what does that have to do with them being actually blind and how is it a mistake? It's like real blind people wearing dark glasses.
No it is not, as the cloths should have been better camouflaged or better makeup. But forgiveness granted for a cult film of its time.
Continuity mistake: During the riddle challenge, Andromeda's hair is in a stylish updo while standing at the altar with her mother Cassiopeia. Perseus enters moments later and solves the riddle. But in the next shot as they enter the courtyard together, Andromeda's hair is suddenly down around her shoulders and she looks like a little girl, instead of the mature woman she was at the altar moments before.
Suggested correction: The next scene is later in the day. Everyone has changed clothes and they are at a celebration.