This is the first time we see Ratchet transforming.
The Null-ray cannon that Knockout wants to give to Starscream as a replacement for his lost arm is a reference to the fact that the Null-ray is Starscream's most prominent weapon in other Transformers cartoons.
When Starscream is back in the Nemesis after returning from the canyon, Knockout asks if he wants a new arm equipped with a Null ray. This is a nod back to his G1 weapon