Board Thread:General Discussion/@comment-26066301-20150518010703/@comment-33336503-20180225030257

Stargazer215 wrote: Okay, I know that the show is over and this reply is a little late, but I was wondering the same thing about why Karai can turn human while mutated and my first thought was “does it had something to do with her DNA?” Well as I was rewatching tmnt for the millionth time, I saw in the episode Karais Vendetta (the one where she got mutated). So she gets captured and shredder sets the trap. Shredder goes to Baxter Stockmans lab and when he goes to ask Baxter if the trap is ready, we see that Baxter is working on the snake DNA to put in the mutagen. He also has what looks like a work in progress retro mutagen because it has the same orangish color. Baxter Stockman gets startled and some of the orange solution spills in the beaker with the snake DNA. And then he pours it in the mutagen vaut that Karai falls into. And that’s why Karai can turn into a human while mutated. And I believe that all of you reading this have seen the show. If not then stop reading now because spoiler.

Donatello does not find a way to turn Karai 100% human.

The episode you're thinking about where Karai is captured and used as bait is not "Karai's Vendetta" but "Vengeance is Mine". And you're right about Donnie not being the one to turn Karai back 100% as Baxter Stockman was able to at some point between "Meet Mondo Gecko" and "The Deadly Venom". Karai already being 'cured' before the "Deadly Venom" even started makes you feel like you're right in the middle of a story rather than the beginning of one and that was just one of many problems laden throughout that episode in particular.