A scene from “Unfinished Business”

Warren "Classic mistake. I may be small, but I’m also very—ah!"

[Leo smacks him and Warren goes flying.]

Leo "Huh?"

[Spinning, Leo swings his sword and slices Warren in two.]

Warren "Uhh."

Raph "Oh, what did you do?"

Leo "He was on my head! I panicked!"

Mikey "Is he gonna be okay?"

Raph "Is he gonna be okay?! He’s in two pieces."

Warren "You fools!"

[They all jump and scream, crowding behind Raph.]

Warren "You’ve unleashed my ultimate power. Now I can—"

Mikey "You can clone yourself?"

Warren "No, I regenerate. It’s an amazing power, but it’s incredibly painful."

Donnie "Fascinating. How long does the regeneration process take?"

Warren "Several days."