Evil Is Sexy: Mandor, the handsome, courteous, and thoroughly manipulative Lord of Chaos.
Fiona verges on this In-Universe. She's one of the most unscrupulous and amoral Amberites as well as a powerful sorceress, and became popular in the Courts of Chaos after the war for these reasons. Mandor himself grew infatuated with her long before they met.
Fridge Horror: Some of the Early Installment Weirdness (the apparently greater violence and psychopathy of the Amberites in the earlier installments) may be due to Corwin being an Unreliable Narrator: as Corwin becomes an accepted "insider" again and the narrator shifts to someone with little experience outside the system (Merlin), everyone becomes increasingly logical and reasonable. If the original interpretation is closer to the truth, even minor gaps and comments in the later works become ominous.
There's a lot of Fridge Horror in the very notion of Shadow. No matter how bad a thing you can imagine, somewhere out there is a world where it's true. The hallucinogenic incident that Luke goes through really calls some of the worst possibilities to your attention.
That moment in Knight of Shadows when the Pattern forces Merlin to basically rape barely-conscious Coral. And here we were thinking that Pattern and Amber are the good guys. Which only goes to show how far outside human understanding the Pattern is.
In the first book, Corwin inspects his brother Bleys' command structure and meets his troops. They are an inhuman, zealously loyal army that Bleys has indoctrinated into thinking of him as one of their gods, at the same time setting up his brother Eric as the "Lord of Evil" in this little religion. Corwin is disquieted at this and realises that Bleys has created an entire army of cannon fodder, and highlights just how exploitable the denizens of Shadow can be.
Fridge Logic: Dara is responsible for setting in motion Brand's plans to obliterate the Pattern. Brand is responsible for setting in motion the invasion of Avalon by Lintra, who bears a child by Benedict who becomes Dara's grandmother. May be justified in that either a.) Chaos time is non-linear, or b.) Dara is a big fat liar.
Possibly Dara's faction was responsible - she does use the pronoun "we" a bit. Possibly she's a time traveller - about the only thing that doesn't happen in the series. Sadly, we'll never know.
Dara's conversation with the Logrus in the tenth book essentially states that she was in cahoots with the Logrus - and therefore presumably an adult - before Brand ever went to the Courts. Which means that the hellmaids' first emergence into Avalon predates the marring of the Pattern - Dara's existence being the consequence of the first while Brand's corruption or manipulation is the consequence of the second. The construction of the Black Road had apparently been going on for much, much longer than Corwin always assumed. Either Dara was an adult before she was conceived, or - and this is more likely - the invasion of Avalon was part of some earlier scheme in Chaos and the Dara-Brand connection was an attempt to exploit the success of that earlier established foothold.
The Merlin series pretty much establishes that Dara is a big fat liar who lies. The simplest explanation is that she lied to Corwin and to Benedict about her origins and she's much older than she seemed in those books. (It's unlikely that Oberon would be fooled about her intentions.) Her walking the Pattern could easily be explained by Corwin being mistaken about the requirements, assuming she doesn't have Amberite lineage through some convoluted means. We know that Dworkin and probably Oberon had to forsake the Logrus to gain the power of the Pattern; Dara could have done this as well and then defected back when she forsook Amber. Another trip through the Logrus could help explain her extra helping of crazy when Merlin runs afoul of her.
Ho Yay: Merlin and Luke. They're closer to each other than any of the women in their lives, and Merlin will always try to see the best in his closest friend. Even when he learns who was really behind the April 30th incidents...
Iron Woobie: Merlin is remarkably well-adjusted considering who his parents are and the place he grew up in.
Magnificent Bastard: Oberon, and several of his children try to match him in this. To the point where Corwin deduces Oberon's presence simply because no one else could pull off a Gambit Roulette that well.
Mary Tzu: Some might regard Benedict's proclaimed abilities as... over the top. Or at least regard Corwin's opinion of him as evidence that Benedict has his brother(s) completely psyched out.
The RPG takes this Up to Eleven, crediting Benedict with abilities that are flat-out impossible for any conventional fighter or general, no matter how talented. Like the ability to automatically parry attacks from invisible, intangible ambushers based solely on instinct.
Memetic Badass: Benedict gets this In-Universe; there are entire shrines dedicated to his aptitude for warfare in the Courts of Chaos. Corwin also gets some of it — the cheat codes in the original Warcraft game were activated by punching in Corwin of Amber.
Moral Event Horizon: Eric burning Corwin's eyes out ends up being a subversion. It wasn't Eric's idea in the first place, and the guy who did suggest it only did so because the maiming, which he knew would only be temporary, was the alternative to simply having Corwin killed.
Brand is offered a Last-Second Chance in spite of everything he'd done up to the point, since he still possessed the means to save the day. He rejects this and then kills Deirdre.
An interesting example with Oberon, who kills and replaces the man he spends most of the first few books impersonating. He also murders Benedict's innocent household servants in order to provoke the reaction he wanted, all to test his children. His apathy and callous killings of these Shadow dwellers is commented upon by Corwin, who at this point in the story has developed a greater empathy for them. For all that, though, Oberon remains the Big Good of the series.
One-Scene Wonder: Rebma, the fascinating underwater Mirror World to Amber, which is often mentioned. It's visited once in the first novel and never again.
Outlived Its Creator: An attempt was made to keep the Chronicles going after Zelazny's death. It was poorly received.