Married with Fishsticks - S5-E15
Revealing mistake: In the scene where "Crustacea" is being hung upside down in the water by the children, you can see her wig detaching on the sides by her ears.
The Convert - S4-E18
Revealing mistake: When Xena is climbing up into the tree, you see a clear shot of her stunt double's face. (00:39:30)
Revealing mistake: In the beginning battle scene, the long shots of Amarice are a stunt double, her face is shown quite a bit. (00:04:35)
Revealing mistake: As Xena watches the dead being put into the wagon, one body is rolled over. You see the man move his arm quickly to shield his fall. (00:25:25)
Revealing mistake: When Xena throws the chahkram at the tree limb, the limb is visibly cut before the digital chahkram slices through it. (00:13:00)
Revealing mistake: When Brutus is capturing Gabrielle, the metal plates on his helmet move, and appear very flimsy. They hardly look strong enough to protect him as a helmet should. (00:13:45)
Is There A Doctor in the House? - S1-E24
Revealing mistake: After Gabrielle's been wounded, there's a scene where she starts thrashing violently. A little after that, Hippocrates declares her dead despite the fact that you can see her breathing in the previous shot.
Revealing mistake: When Marcus is hanging off a wall in Hell and under attack from a harpy, there's a shot of Xena jumping on said wall to help him. When she lands, you can see the pavement give in a little, like it's made of rubber instead of stone. (00:35:45)
Revealing mistake: When Xena is fighting Celano, right after he grabs his knife to try and kill her, the shot changes to Xena, who after dropping back to the ground is supposed to be unsheathing her sword, but actually has it out already and just pretends to. (00:39:00)