Retromutagen Ray Generator, a device that undoes mutations. Shredder uses it in the 1987 TV series, Archie Comics and the 1987 video games. In the 1987 TV series episode Shredder & Splintered Shredder displays what appears to be a ray gun and explains that it is a Retro-Mutagen Ray Generator - a device that undoes mutations. He suggest that it is the only thing that will transform Splinter back into Hamato Yoshi and invites them to "come and get it." The Turtles are more than anxious to accept Shredder's offer, however, Splinter suggests that he alone must go after Shredder for fear that he might use the Retro-Mutagen Ray Generator on the TMNT - thus transforming them back into ordinary turtles. Splinter sneaks inside the Technodrome to find the Retro Mutagen Ray Generator.
Splinter discovers that the Retro Mutagen Ray Generator is actually just a hologram. Once again the Sensei has been duped by Shredder, who tells him if he wants the Retro Mutagen Ray that he must first taste his blades, and once again Shredder engages him in marital arts combat. Krang feels ill-prepared to handle the "boys in green" by himself, so he summons Shredder. With the flip of a switch, Shredder imprisons Splinter in an electric cage and disappears to save Krang. Fearing that Shredder will use the Retro Mutagen Ray Generator on the Turtles in his effort to save Krang, Splinter uses one of his long fingernails to remove a metal screw in the floor, heaves it through the electrical cage and destroys its generator.
Up on the streets, as the Turtles are about to be reverted to their natural state, Splinter arrives in the nick of time and hurls his staff at Shredder, knocking the Retro Mutagen Ray Generator out of his hands and destroying it. While the Turtles thank Splinter and sadly acknowledge that the RMRG was his only chance to become human again, Shredder and Krang escape back to the Technodrome.
In the 1989 video game Shredder fights using the Life Transformer Gun, which de-mutates and instantly kills the Turtle that the player controls. He also takes away roughly half of the player's health if he is touched. After he is defeated, the Shredder turns into a pile of ash and the Life Transformer Gun is used to turn Splinter back into Hamato Yoshi.
In the arcade game Shredder has access to a similar attack where he shoots an energy beam that instantly kills any player it hits by causting them to de-mutate into a regular turtle.