Worlds Collide: Part 3 - S3-E6
Plot hole: In their previous encounters with the Triceratons, the Turtles had to learn the hard way that the Triceratons breathe not oxygen but a combination of nitrogen and sulfur, which is detrimental to most Earth lifeforms, and thus had to wear special rebreathers. When the Turtles, Splinter, April and Casey enter Zanramon's throne room along with Traximus, none of them wear any breathing equipment to protect themselves from the hostile atmosphere.
The Lesson - S3-E13
Other mistake: Donatello is briefly replaced by a second Raphael when they're sitting at April's apartment's table.
Continuity mistake: When they first enter the Y'Lyntian city and are attacked by the Lava Wraiths, Raphael gets his sai melted by them. But after taking their goodbyes from Versallia, Raphael has his sai stuck back in his belt.
The Real World: Part 1 - S3-E22
Other mistake: When Hebi learns of the Mogura (mole) Ninja's failed attempt to capture their prime target, Lord Noriyuki, the Ninja leader who delivers Tomoe Ame to him speaks only of "interference". But when Chizu is called forth, Hebi commands her to deal with the kame Ninja (meaning Leonardo) even though his presence was not verbally mentioned beforehand.
Other mistake: In the scene where Raphael and Michelangelo report from their ceiling vantage point, we see a hallway full of Foot ninjas. Strangely, we can see a brief shot of an Earth Protection Force trooper walking peacefully among amongst the Foot even though they are hostile to them. (00:07:50)
Answer: Per Wikipedia, the series originally aired in the US on Fox for its first six seasons from February 2003 to October 2007. However, the main storyline of the series ended after season five. Following this, the show was retooled with a new art style, comedic tone, as well as a new storyline. The show moved to the CW for its final season and aired from September 2008 to March 2010. However, it would not officially end until the broadcast of the TV movie Turtles Forever, which was produced in celebration of its 25th anniversary, and served as a series finale for the show.
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