How many times was an anti-mutagen invented?
 

So I just watched Michelangelo's Birthday (aka "the one where Shredder looks like he needs to poop real bad"). The plot revolves around Krang having invented an anti-mutagen which Shredder tries to use on the turtles. Ironically, I can think of at least three other episodes featuring the invention of anti-mutagen, how many were there?

*Shredder & Splintered (Retromutagen ray)
*Splinter No More (Donatello)

Michaelangelo's Birthday has one of my favorite scenes of the show, where Shredder/Bebop/Rocksteady enter the Turtle Van with the Turtles but Raphael shoves Bebop/Rocksteady out saying, "We'll put up with you Shredder but not your mutants."

And Shredder says, "You win a few, you lose a few." James Avery's deliver on that line was perfect.

Also, "The Gang's All Here" with the cookies that turned Michaelangelo into a human. However, the formula was unstable so he kept changing back.

The retro mutagen ray gun appeared twice more after The Shredder Is Splintered. It was taken from Shredder after he reconstrcuts ir in to counter the effects of Baxter's insect/arachnid mutations in Revenge of The Fly. After the turtles revert everyone back to normal they keep it. Interestingly enough they do not use it on Splinter after this and it is still working in its last appearance, Wrath of The Rat King. In that episode the turtles used it to reverse the new kind of mutagen used on Rat King's royal guard.