The man watched with impassive interest as Elias screamed again and turned to run. He never reached the door. Agramon surged forward, his dark mass crashing down over the warlock like a surge of boiling black tar. Elias struggled feebly for a moment under the onslaught—and then was still. (Prologue.23)
We begin the book with a pretty graphic violent act, as a demon kills an unsuspecting warlock. What's even more horrific is that Valentine does nothing. This kind of violent sacrifice is exactly what he needs.
Jace had wanted the oblivion of fighting, the harsh diversion of killing, and the distraction of injuries. (1.1.12)
Jace doesn't know how else to deal with his problems. He's the type of guy who needs to break stuff to vent some anger.
[Maia] remembered the dark shape exploding out from behind the metal merry-go-round, the huge wet wolf body knocking her into the mud, the savage pain as its jaws clamped down on her throat. (1.2.4)
In this world, it's impossible to experience any sort of peaceful change. Maia's werewolf curse has a violent beginning, just like Simon will experience later when he becomes a vampire.
The Shadowhunter boy was standing on the bar, feet planted wide apart. He really did look like an avenging angel getting ready to dispatch divine justice from on high, as the Shadowhunters were meant to do. (1.2.62)
"As the Shadowhunters were meant to do" implies that Jace is genetically predisposed to violence. Maybe there's no other way for him to behave, no matter how hard he tries.
[Brother Jeremiah's] previously sewn-shut mouth gaped open in a soundless scream, the gory threads of torn stitches dangling from his shredded lips. Blood, black in the torchlight, spattered his light robes. (1.5.12)
Yikes. This is another graphic, violent scene, which by this point is Valentine's M.O. When he's teamed up with his fear demon, something bad is bound to happen.
She couldn't not look at the blood matting Simon's brown hair, his torn throat, the gashes along his dangling wrists. (2.9.123)
Here's Simon's vampire transformation that we alluded to. You never expect a vampire transformation to be full of rainbows and sunshine, but this one is pretty bloody.
[Simon] took a step toward [Maia] and her hand whipped out, nails shooting out like talons, suddenly impossibly long. (2.12.47)
Maia accuses Simon of being less than human, but she's even more inclined than Simon is to lash out with violence at something she doesn't understand.
Fighting to [Jace] was like sex to other people. (2.12.85)
Um, this is a red flag, girls. If anyone describes a guy like this, you probably do not want to be in a relationship with him.
With a sharp flick of his wrist, he brought the Sword level and slashed it with a single smooth gesture across Simon's throat. (3.16.184)
Poor Simon, he gets subjected to more violence than almost anyone else in this book. As if the emotional pain wasn't bad enough…
It struck the demon, slicing off the top of its skull the way you might slice the top off an egg. (3.17.184)
This is some graphically violence imagery we can get behind—the image, not the violence. Don't try this at home, kids. There's nothing that isn't exciting about a bloody demon fight, especially when the good guys are winning.