Some might say that given this character's relatively dark aesthetic even before being possessed by a demon, that there wasn't much that needed to change. But the subtle changes are there. The stubble, the messier hair, the more formal clothing, it's all very much out of character for Jace. Jace is already a pretty dark character to be sure but he is still basically just a boy, barely into his 20s. Before the possession, all of his features and style points to his youth (read: innocence) the demon corruption pushes him farther into adulthood hence the facial hair, longer locks and crisp suits. Still hot though.
Luke: You know, I’m proud of you, Kiddo. It’s not every day you get an angelic rune. Pick your weapons yet? Clary: Yeah. [She shows the first blade] Clary: What is it? Luke: That was your father’s dagger. Clary: What?! Luke: You didn’t know? Clary: I didn’t know. I had no idea. [She shows the second dagger] Clary: I choose this one too. Luke: You don’t choose the blades. The blades choose you. That one was Jocelyn’s. Clary: What? Luke: They’re both part of you, Kiddo. The light and the dark, whether you like it or not.
Simon: What are you planning on doing to me? Seely Queen: Relax. Simon: Come on. You guys really had to tie me up to vines again? Bad memories. Seely Queen: It is this way, so that you don’t reflexively squirm. Meliorn: It is ready, my lady. Simon: Why are you going to hurt me? I’ve done everything you’ve asked, I’m a good guy...I sang you a song about nature! Seely Queen: Don’t not fret. The hurt will be over before you know it. Simon: So, this is it? This is the end? This is the end?! Seely Queen: Proceed. [Seely spins around the sticks] Simon: What is that? What are you doing?! [Simon screams in pain as the rune is applied]