Continuity mistake: Up until Green No More in Series 2 (where the Green Ranger powers are destroyed), the Green Ranger's overshield constantly changes between solid-looking metal to flimsy-looking cotton. This is the most obvious difference between the Japanese and US footage.
Continuity mistake: When the Villains send their cronies (for example, Putties, Tengu Warriors, Cogs, Piranhatrons, etc.), their numbers constantly change from when they arrive, to when they leave. This is due to the use of Japanese footage used from Kyoryu Sentai Zyuranger.
Other mistake: Episode 13-12: "Shadow (2)." When Cruger is challenged to defeat 100 robots, a red countdown meter appears on the screen, ticking down each time Cruger dispatches an opponent. When the counter is at 21, Cruger slices his sword at a robot, which then goes down. But the counter stays at 21 and only goes to 22 when he slices at the next robot. Every robot in the sequence goes down after a single hit from Cruger's sword.
Plot hole: Somehow Bulk and Skull know that the Rangers use the phrase "It's Morphin' time" and also reach behind their belts. They're not supposed to know this, unless they know the Rangers' identities (which of course they don't know despite their "efforts").
Continuity mistake: When in Tank mode and Megazord mode, the order in which the Rangers sit is: Billy, Trini, Jason, Kim, Zach. When switching between Tank mode and Megazord mode, Trini and Kim are switched - they are then back to their original seats once the Megazord has been formed.