The One With the Sharks - S9-E4
Revealing mistake: While Monica and Rachel are talking about Chandler's "jollies to Jaws" Rachel's wearing a colorful flowery top, and after Joey walks in just as Monica takes her seat at the table in the closeup, it's Jennifer Aniston's stand-in, wearing a blue top, who is seated beside Monica. And Rachel's hair is waivy in the flowered top, but straight in the blue top. (Viewed in widescreen).
Super Grover
Neogenic Nightmare Chapter 11: Tablet of Time - S2-E9
Continuity mistake: When Dr. Connors starts transforming into the Lizard after being blasted by the robot, the sleeve of his lab coat magically becomes tattered at the same time his hand transforms. Subsequent shots also alternate with his sleeve being tattered and pristine as well as his hand being reptilian and normal.
Phaneron
Continuity mistake: When Mandarin pulls the lever to initiate the decomposition sequence, the jewels on his rings are shown to take up about half the width. When the shot changes, the jewels are suddenly as wide as the rings themselves, if not wider. (00:18:20)
PhaneronThe Origin of the Fantastic Four: Part 2 - S1-E2
Continuity mistake: As soon as Slash starts the jailbreak, the heavyset inmate suddenly has darker skin, which then reverts to its normal lighter shade when he is running towards the camera. (00:03:10)
Phaneron