This scene is from Keith's Dark Vision part 3 where Lucifer is about to transform into his new form while in Lelouch's body.
Lines
Lelouch: (dying) So...this is...how it ends huh?
Duskmon: Afraid so. Now Lucifer will never control you.
Lelouch: That's... where... you're wrong... Duskmon...you see...Lucifer... is...me. (dies)
Duskmon: What?! Oh no, NNNNNNNNNNNNNOOOOOOOOOOOOO!!!!!!!!!!!!!!!!!!!!!!!!!
Aaron: It's too late!
Soon Lelouch's body begins to change as Lucifer's spirit takes hold. And with a sudden flash of light...
KA-BOOM
Lucifer emerges in his newest form.
Aaron: Lucifer.
Lucifer: So, what do you think of the new and improved ruler of Darkness?
Jake: I'm not even going to answer that question.