Retro-Mutagen

Donatello  created an adtidote to the Mutagen by using April's unique DNA.

Donatello also stated that it takes ten canisters of Mutagen to make one dose of Retro-Mutagen

History
In The Lonely Mutation Of Baxter Stockman the Turtles tried to use the first dose to cure Kirby O'Neil, but after a brief fight with the now mutant fly Baxter Stockman the canister broke. Stockman held April for Randsom for the second and last dose of Retro-Mutagen they had. After a fight with Stockman and some Foot-BotsThe canister shatters, although April did not lost any hope and she pulls the wings back on her father and she makes him go underneath the spilling fiasco, where the last drop of Retro-Mutagen on his head and he reverted back to his normal self.