Darkness-Induced Audience Apathy: When exactly it sets in is up for debate, but odds are you'll get hit with it somewhere. Most likely Annabel's death, combined with Helen getting away scot free, which serves no real purpose to the story.
Designated Hero: Mae in Surrender, where she spends the whole book gleefully trying to steal Sin's birthright. And succeeding.
Dropped a Bridge on Him: Annabel is randomly killed off just when she starts to become really interesting, for no other reason than so Jamie and Mae can spend the last book as orphans together with Nick and Alan. Then in book three her killer becomes a Karma Houdini, rendering it even more pointless.
Esoteric Happy Ending: The magicians and the Goblin Market join together...except many if not all the magicians are still just as evil and will likely soon take down the Market from the inside.
Ho Yay: Nick and Jamie - Mae even suspects Jamie has a crush on him.
Les Yay: Mae and Sin, oh so much. From Mae's obvious girl-crush to Sin's more subtle flirting. Can't forget Liannan twirling about there:
Mae: What else do you want? Besides the obvious.
Liannan: I want a kiss.
Mae: A - a kiss?
Sin: A kiss? I have a certain amount of expertise on the subject.
Mae: No. You can have your kiss. I'll do it.
Liannan: I'll keep you both in mind for later. But I don't believe I mentioned who I wanted the kiss from.
Ship Mates: Mostly this depends on which brother you'd prefer to see Mae with, but most commonly Alan/Sin to Mae/Nick.
Unintentionally Unsympathetic: Seb talks a big game about still being a nice guy even after being revealed as a magician, but in practice he comes off as being just as bad, including not one but two scenes where he has no objection to his allies threatening to kill a little kid. It ultimately takes an action even the other magicians think is wrong to get him to put his money where his mouth is.
Also, Helen is supposed to be seen as a Worthy Opponent whose Heel–Face Turn should be praised. Except there's that time when she pointlessly and heartlessly murdered Annabel, which makes her come off as a Karma Houdini instead.
The Woobie - Jamie in Lexicon has got to be in the running for Woobiest Woobie to Ever Woob. By the end of Covenant,when he, in conjunction with Nick, proceeds to wipe the floor with some of the Obsidian Circle, he's a lot less vulnerable and a lot more grown-up...but he still needs a hug. Badly.
Hell, Nick and Alan themselves fall into the Woobie category.....