Death by Irony: Not only is Metalhead taken down by his own creator, he's also destroyed by the very same weapon that Donatello's dissatisfaction with led to Metalhead's creation in the first place.
Foreshadowing: Leonardo watches an episode of Space Heroes where Captain Ryan has to Mercy Kill one of his crew after a brain-like alien takes over his body. This foreshadowed Metalhead being taken over by one of the Kraang and Donatello defeating Metalhead by damaging it.
Funny Background Event: At the end of the episode, whilst Donatello is showing off his, erm, rocket-staff, in the background you can see Raphael get annoyed at Leonardo, and grab him in a headlock with Michelangelo trying to pull him off.
Inventional Wisdom: In hindsight, using a Kraang interface port for the top of Metalhead's head wasn't that good an idea.