Break the Haughty: Last Stand of Dead Men. First she finds out about Ghastly. Then Stephanie tries to kill her and drives her out of the house. Then she kills someone in a fight. Then Darquesse takes over, seemingly for good.
Heroic BSOD: Has a minor breakdown in Last Stand of Dead Men after Stephanie tries to kill her and drives her out of the house, but she goes practically catatonic after killing a woman in a fight. Darquesse takes full advantage.
Hormone-Addled Teenager: Davina Marr accuses her of this and being smitten with Skulduggery in Dark Days, but it's more prominent from Death Bringer onward.
How Much More Can She Take?: Lord Vile slits Darquesse's throat, shoves his thumb in her eye and generally delivers a No-Holds-Barred Beatdown that leaves her on the brink of death. She pretty much walks it off. On one hand... yay! Skulduggery didn't kill Valkyrie! On the other hand... Darquesse. Just. Doesn't. Die.
In Kingdom of the Wicked she survives her heart being crushed, her jaw being burnt off and beheading.
Off with Her Head!: Courtesy of Mevolent. Luckily, she was Darquesse at the time. It didn't take.
Omnicidal Maniac: Darquesse is prophesied to be this, but has mainly restricted herself to tearing apart people who are trying to kill her or in her way. She outright stated that she doesn't want to destroy the world because "it's funny.".
One-Man Army: Darquesse literally takes out an entire army in Last Stand of Dead Men.
Self-Fulfilling Prophecy: Sealing her name pretty much gave Darquesse free reign when a Remnant tried to possess Valkyrie. Thankfully, it didn't last. Whether or not this trope is completely subverted remains to be seen.
Ax-Crazy: While he seems perfectly normal (aside from the obvious lack of flesh and organs) a few people, including Skulduggery himself, have alluded to him becoming a bit of psycho after his family died. It started to show after Dark Days.
Don't try to manipulate Valkyrie, don't threaten Valkyrie, and for God's sake don't harm Valkyrie in any way. Best just leave her be. A few people have told Valkyrie that the only reason she isn't dead yet is that people know how Skulduggery will react. This ends up saving her life in Kingdom of the Wicked.
Would Hurt a Child: He attempts to shoot Kitana out of necessity more than anything else in Kingdom of the Wicked. He is, however, unwilling to use lethal force on the young recruits that the American Sancturary has blocking their path in Last Stand of Dead Men.
Heroic Sacrifice: Subverted in Last Stand of Dead Men. China uses a particular spell devised by Mevolent, of all people, to burn herself alive in an attempt to take down Madame Mist, which succeeds. However, even after a Dying Declaration of Love to Skulduggery, she survives thanks to Darquesse's intervention.
The Vamp: Has her moments. May have been one before she turned "neutral."
We Used to Be Friends: As of Death Bringer, Skulduggery is seriously pissed off with her to say the least. Valkyrie's not too thrilled with her either. She's amicable with Valkyrie by Last Stand of Dead Men and seems to have reached some kind of understanding with Skulduggery, even if he can't forgive her.
Dating Catwoman: So far his love interests include Darquesse (the harbinger of the apocalypse), Myra (an Australian assassin who is trying to kill him), and Stephanie (a murderous Ambiguously Evil reflection). Dude cannot catch a break.
Ambiguously Evil: Gets steadily creepier as the series progresses, and ultimately murders Carol and tries to kill Valkyrie. But in Last Stand of Dead Men she gets a Sympathetic P.O.V., starts fighting to protect her family and is clearly smitten with Fletcher.
Valkyrie starts treating it a lot better in Kingdom of the Wicked out of loneliness. She's outright stated that she considers it a person now. Unfortunately, it agrees.
Reflection: I'm not a thing. I'm not an it. I'm a person. I'm a her. I have a family who loves me. I have parents and a little sister who I'm going to take care of. I have friends in school, and I want to go to college. I want a normal life. A happy life. A life. And I'm going to take it.
Faux Affably Evil: Re-read the part where he's having his little moment with Skulduggery. If it weren't for the fact that Skulduggery was chained to a chair, it almost would seem like they really are, as Skulduggery puts it, "two guys chatting."
Squishy Wizard: Has some very formidable, very scary powers that he's all too happy to use on people...and then he goes and gets his ass kicked by Skulduggery whenever forced into close-combat. Repeatedly.
The Starscream: In the alternate universe. betrays both Mevolent and China
Back from the Dead: Sanguine kills him in Dark Days after finding out he's not a killer, but Scarab decides they may as well put his death to good use, and makes him a zombie. Then in Kingdom of the Wicked he gets Dr Nye to bring him completely back to life. See Gender Bender.
The Worf Effect: He's a completely unstoppable badass, who lasts all of five seconds against Lord Vile before he's ripped apart.Similarly, the Black Cleaver beats the crap out of Skulduggery until he uses Necromancy.
Friendly Enemy: Seems to be on these terms with Valkyrie after the operation.
Graceful Loser: After operating on Valkyrie during life-threatening circumstances, it seems to take it rather well considering the fact that it lost an opportunity to look for a soul (And y'know, the fact that he threatened to kill her).