Is there a reason April's mutation could be cured at least 3 times but not Splinter?

[neatoman]

Aside from "Because that's what their toys look like" of course.

And before you say it failed in that one episode or that April was mutated in different ways, let's point out that Irma and Vernon were also turned into rat mutants with Krang's mutagen (even if there was an unexplained "instability" in that episode that was the cause behind the impermanence). That and there is idiotic crap like treating the destruction of the anti-mutation ray gun as if another one couldn't be built with literally no reason to think it couldn't be done or Splinter deciding that living a sewer is better than paying cab fare.