Theory on Subprime's Cybernetics
 

I like to theorize on how Subprime got those cybernetics in the form of a headcanon

Subprime was there when the Mrs. O'Neil clone was created. That shapeshifter caused a lab accident that somehow scared Subprime. That's why it was deemed too dangerous. Shortly afterwards, Subprime has been put under medical attention. In a reference to Star Wars Episode 3, he has been implanted with cybernetics, due to sever injuries. Under Kraang Subprime's orders, The Kraang lies to Mom-Thing (as Raph later calls it) about still needing it. It worked, and the experimental shapeshifter is frozen, and the Kraang ship got shut down. As a way of Subprime saying to never speak of this scaring incident again.