What an Idiot!: Blake turning Joey into a Night Thing without knowing the countercurse.
He doesn't learn his lesson even after that. Courtney takes him and the other kids to the land of the Night Things, after the others beg her to help Joey. She, as the only one who's been there before, tells them they should go around the most populated areas. Blake decides that it's best to barge right through the middle of town, deciding that it's like "The Lord of the Rings meets Disneyland." The other kids hesitantly follow, leading to them all getting captured, and most of them being put in extreme danger.
Skarrow, who left his home and adopted mother so he could be with Hermia. He ends up being blamed for cursing her and killed not several feet from his mother. Making things even worse, it's implied that Hermia could have found a loophole from the curse silencing her to name the person who bewitched her, but didn't bother because "[she] just wanted to be left alone."