Revealing mistake: Certain monsters in Zord battles were designed for the first series. This is so Saban could use Japanese footage of ground fights, to save on shooting their own (As the costumes from series 1 carried over into series 2). Sometimes, you can see the Megazord, and Dragonzord, getting attacked (you may need to pause it). It should be the Thunderzord, or Tigerzord.
Other mistake: After the teens leave the command center, Rita sees this and orders the creation of her Putties. Her henchman slaps down a few things of clay into a mold loosely, that then show the perfect figurines of the putties coming out of them. However with the shape of the mold, there is no way that the clay would come out in shapes like that or with that detail. (00:11:35)
Continuity mistake: At the start of the episode, Bulk attempts to climb the rope and breaks it, pulling it down with several pieces of the ceiling coming down on top of him. At the end of the episode, this is suddenly all fixed with Trini climbing the same rope. The same gum and dirty spots are all around the top again with the ceiling appearing completely undamaged from before despite Bulk yanking it free and breaking the ceiling. (00:19:25)
Revealing mistake: For shows like this, sped up footage can be used for effect on people or items to make them seem like they are going faster. However, in the Command Center after Alpha accident'y zaps himself, he starts to flail around the room rapidly with sped up camera. The rangers move out of the way at seemingly normal speed which would mean they were actually moving slowly when filming to make it appear they were normal. This is a good effect, except the sped up camera is given away by the fact the fluctuating lights on the golden poles around the room are flashing at much higher speeds by the sped up footage, giving it away. (00:05:12)