Shredder was going to punish Baxter Fly for betraying him. So Shredder requested Baxter to make one last mutation. Later on, Baxter Fly created a serum with the DNA of a serpent. This became known as the Mindless Serpent Serum.
When this serum is in Mutagen, an organism that falls into the Mutagen with the serum in it can mutate into a mutant. But the organism will mutate into a mindless mutant snake.
- The color of the serum is purple.
- Because of the purple color, it might have dyed Serpent Karai's armor to make it have a purple color, instead of it being silver like it did when she was her human self.
- While Baxter Fly was making it, an orange substance fell inside the serum, which might have possibly been Retro-Mutagen, by the fact that Serpent Karai is able to shape-shift into a snake/ human.
- The serum was targeted for the Ninja Turtles.