The Phoenix Saga (2): The Dark Shroud - S3-E4
Continuity mistake: When Gambit is getting ready to attack Dark Xavier, the ticket booth behind him is unoccupied. When Dark Xavier deflects Gambit's kinetically charged playing card to the ticket booth counter, a man is now inside the booth. The bottom center window also goes from being closed to being open. (00:12:16)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Continuity mistake: The tops of Juggernaut's boots change from brown to orange after he bursts into Professor X's room. (00:20:30)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Continuity mistake: When Cyclops and Wolverine bring Jean back above the water surface, her wet hair is pointing straight down. When the shot changes, her hair is suddenly wavy and parted over her forehead. (00:05:00)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Continuity mistake: When Xavier and Cyclops begin arguing in the hallway, the door and doorway to Jean's hospital room are visible over and behind Xavier's right shoulder, and a chart is a few feet to the right of the door. A few shots later when Cyclops is telling Xavier that he failed to warn everyone, the chart is still visible, but now the door is missing, with the wall now appearing to be longer. (00:06:40)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Revealing mistake: When Jean is saying that she feels strange, the edge of an animation cel is visible moving left and right under her pillow. (00:05:27)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Continuity mistake: When Gambit is knocked into the hot dog stand, he is lying on his stomach with his left arm tucked and his right arm bent at the elbow. When the shot changes, both of his arms are now outstretched. (00:13:37)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Continuity mistake: When Dark Xavier knocks Cyclops into the wall, it leaves a small hole. When Cyclops gets up, the hole is now larger. (00:14:47)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Continuity mistake: When Xavier is looking out at Banshee and Moira from the window to his room, he is facing the window directly. When the shot changes, his left profile is now facing the window. (00:17:31)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Continuity mistake: When Lilandra first appears in Xavier's room, she appears to be around 7 feet tall. She is nowhere near that tall in subsequent shots. (00:18:29)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Continuity mistake: When Xavier lands his plane on the Muir Island helipad, the nose of the plane is directly to the right of Banshee. When the shot changes, Banshee is now standing a few feet in front of the nose. (00:17:01)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Continuity mistake: When Xavier is looking at Moira and Banshee from his window, as the camera zooms in on the latter two, you can see they are facing each other, and Moira has her left arm on or near Banshee's hip. When the shot changes, they are standing side by side, with Moira's arms wrapped around Banshee's left arm. (00:17:41)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Revealing mistake: When Lilandra is saying to Xavier "I have seen your face a thousand times in my mind," the edge of an animation cel is visible around the parietal area of Xavier's head. (00:20:24)
Answer: Chris Potter, the original Gambit voice actor, did indeed quit the role in the 4th season. His last episode was The Phalanx Covenant Part 1 so it seems reasonable that Fox would limit the use of the character even though it was recast. It doesn't appear that Potter left the role due to animosity, he stated in an interview that he wished to play Gambit in the first live action X-Men film.
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