#because normal kraangification contamination doesn't work on him

[hyperfixatinator]

Yo! Overthinking at 3am made me theorize about Donnie and how a certain injury might have become a key part in saving the world!

Firstly, let's talk about Shredder's energy, particularly about how it's pink.

Karai's flashbacks to her father meeting an "oni" reveal that the Shredder armor was created by the Kraang. So Shredder's energy is basically raw Kraang energy, without the centuries Yokai have spent molding it into what's now called "Mystic".

You remember the Shredder fight at the docks where he clawed right through Donnie's battleshell, right?

After the fight's over, the claw marks on his shell are glowing pink, like Shredder's Kraang energy.

I doubt Donnie designed the insides of his battleshell to glow a bright pink, especially when it's so heavily damaged. I believe it could be the residual energy from Shredder's attack interacting with an open wound that attack caused.

What if it's Donnie's mystic energy fighting off the foreign pink energy, like an immune system fights a disease? And like an immune system creating antibodies to keep that disease from taking hold again, he became resistant or even immune to Kraang infection after he healed?

Maybe this is how Donnie was able to pilot the Technodrome with little-to-no struggle for control. His body came prepared with a resistance/immunity that prevented the Technodrome from rejecting or kraangifying him instead.