Some ghouls attack and kill two sixteen-year-old Wardens-in-training (and is implied to have raped one of them while doing so). Harry proceeds to tear one in half and then roast what's left alive, then throw the other one into a pit, melt the sand around it into glass, then pour orange juice on its head so it'll be eaten alive by ants. Carlos eventually convinces him to have mercy on Ghoul #2 and shoot it in the head, but it's still a shocking scene.
When he shows Molly that she isn't ready to help him by letting a miniature sun slowly drift towards her head, just to give her more chances to try and fail. While taunting her for not being able to stop it.
Just before this, he slags a trash can and tears up a sidewalk, causing significant damage to a couple storefronts, just 'cause he's frustrated.
The prelude to Harry challenging his enemies, when they're going down to the depths on House Raith's property and the path is lined with hundreds of kneeling humans the White Court has enslaved, silken threads around their necks and tethered to the ground to show their utter subjugation, decked out in kimonos, placidly waiting to be fed upon by the guests. And there are already several empty spaces where a vampire has 'overindulged'. It's one of the most disturbing and chilling sequences in the whole series.