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.
Revealing mistake: When Rita is shrunk and put into her travelling vessel, the shrunken Rita is a very bad model. (00:12:20)
Visible crew/equipment: Just as the Rangers find a way to defeat Lord Zed's putties, we see a camera shot circulating the rangers. Pay attention and you will see that there is one shadow on the ground that doesn't move. Clearly from a member of the film crew. (00:16:40)
Visible crew/equipment: When the Pink, Green, Black and Red rangers teleport to take on the monster, we see the Pink ranger walk towards the camera. As she does, so the stage lights are reflected in her helmet. (00:13:30)
Revealing mistake: When the Dragonzord returns to the sea, the shot is reversed. Watch the water. (00:09:30)
Visible crew/equipment: At the very start, Zack hands Billy some glasses which he puts on. They reflect the stage light in front of them perfectly. (00:01:10)
Visible crew/equipment: After the Iguana changes back, the camera pans up from the floor and you can see the camera shadow moving up Billy's leg. (00:18:10)
Continuity mistake: Billy takes Kim's mirror, and it has an blue backing. After Billy morphs, the mirror now has white markings on the backing.
Plot hole: During the Green Candle, in series 1, we are told that the only reason Tommy's Green Ranger powers could be drained is because he touched a special wax. However, Kim, Billy, Zack, and Trini did not touch the special wax, therefore the candles shouldn't have stolen their powers. When they were captured, they were transported straight to a prison cell as Goldar lit the candles, therefore the Rangers couldn't have touched the candles when captured.
Suggested correction: Different candles. A different idea. Just because they did things one way, one day doesn't mean they absolutely have to follow those rules the second time and apply to different people. They could have changed the plan.
Continuity mistake: When Bulk and Skull are waiting out the appearance of the Rangers, Bulk's kneepads are just below his knees. When he goes to grab Skull (after the explosion), they are around his ankles. When they arrive at the explosion scene, they are on his knees.
Continuity mistake: This can only be seen for a few frames, so slow motion may be needed. Tommy reveals himself as the White Ranger by unclipping his helmet; however, his ponytail is already visible. Tommy's hair should have been inside his suit/helmet if he had just unclipped it. From behind shots, it is tucked in.
Other mistake: The Tigerzord has various orbs behind the White Ranger, that give the Tigerzord various abilities. The only one we ever see used is the one for a Fireball. For the rest of the series, this orb disappears and reappears, whether the Fireball has been used or not.
Revealing mistake: The giant tin opener Bulk and Skull use to try and open Rita's dumpster is not metal at all - you can see the handle flopping over. It is more similar to Styrofoam.
Two for One - S2-E19
Character mistake: After Tommy and Kimberly are attacked by Pursehead, when they morph, Tommy says "Dragonzord" instead of "Tigerzord".
Other mistake: When Tommy is ambushed by the putties, he kicks one which explodes despite the fact that the Z on the puttie's chest never glowed white like they always have in previous episodes.
Audio problem: When Tommy is fighting the last putty before Goldar transports him, there is a contact noise made as he rolls over the putty's back; no hit was made on that manoeuvre.
A Monster of Global Proportions - S2-E25
Deliberate mistake: A few deliberate mistakes here. It was around this time that 3 of the actors on the show (Austin St. John, Walter Jones, and Thuy Trang; who played Jason, Zack, and Trini) walked out over pay issues. So, to work around this until replacement rangers could be found, Saban used old footage of the 3 that walked out. The mistakes are as follows: 1) Tommy is shown to be wearing green. The Rangers wore clothes that matched the colour of their powers - Tommy was now the White Ranger (and should be wearing White clothing), as the Green Ranger powers had been destroyed. 2) Zack's hair changed from dreads, to his flat cut. This had an instant effect on Kimberley and Tommy's hair (again, due to the old footage), which had gotten noticeably longer as the series progressed. 3) Jason, Zack, and Trini's voices were different when they were morphed - obviously, they were voice sound-a-likes.
Zedd Waves - S2-E26
Continuity mistake: Beam-Caster's colour changes 3 times during the episode, It starts as and a orange body with a blue cape, to a black body and black cape. then later back to orange body and blue cape, and finally back to all black clothing again.
Zedd Waves - S2-E26
Other mistake: After the shot changes from Zedd yelling at Goldar to Tommy, Kim, and Billy in the park, for a brief second, you can see the three actors were standing and waiting for the cue to begin walking; most noticeably with Tommy who puts a little jump into his first step from standing.
Return of the Green Ranger (2) - S2-E45
Factual error: Billy, Kim, Rocky, Aisha, and Adam return to Angel Grove in the 1700's...and there are British Redcoats there. On the West coast, in California. England never deployed troops to California, especially considering it was part of the empire of Spain at that time.