Continuity: As Talos lifts the Argos, sailors are seen falling from a ship that is obviously still in the water.
Revealing mistakes: As the first harpy appears to torment Phineas, the wire holding it up is visible.
Continuity: When the crew are being recruited, Hercules' arms are alternately crossed/uncrossed between shots.
Continuity: When Jason is being held in the Hydra's tail, he strikes the tail with his sword, but the sword bounces off the tail as if the tail is made of rubber.
Continuity: In the opening battle scene, some of the streets appear wet with rain, while others are dry.
Continuity: Before Hylus hurls the discus, he hands his pack to a bystander. After hurling the discus, he is shown in close-up with the pack still slung over his shoulder. In the following scene, the pack is once again missing.
Anachronisms: In the scene where Medea is performing, she turns around only to reveal her dress has an obvious zipper. Zippers weren't invented until the mid to late 1800s.