Anti-Climax Boss: After four books of build-up, the Shaggat is dealt with summarily when Neda snaps his neck with a well-placed kick while he's chained up but gloating. However, the fact that shedoes kill the most feared and hated man in recent Mzithrini history so casually basically causes all the other Mzithrini to regard her as a certified badass.
Arunis is an immortal, sociopathic, manipulative sorcerer who set most of the immediate plot (including the coming world war between superpower empires and the retrieval of an extremely dangerous Artifact of Doom) in motion to further his own ends. Those ends turn out to be arranging the destruction of the world as an offering to the Night Gods, so that they will be impressed enough to elevate him to godhood himself. In pursuit of this goal, he kills, tortures, and Mind Rapes his way across two continents, including sacrificing his own (few) loyal minions for short-term advantage, all without the slightest whiff of remorse. His in-universe reputation is well-earned. He even manages to make trouble post-mortem, with his ghost mind raping one man to the point of completely destroying his personality while trying to possess him. Guy was an Asshole Victim, but still.
Macadra is Arunis's rival, on-and-off co-conspirator, peer in age, power, and wickedness, and his sister. She wants the same Artifact of Doom he does, though she intends to conquer the world rather than destroy it. Her handiwork is mostly plainly visible in the fate of the Empire of Bali Adro, whose throne she subverted centuries ago, in the process turning it from a prosperous, enlightened society to a totalitarian hellhole (much to the horror of the time-displaced Bali Adrans traveling with the protagonists). Like her brother, she's The Dreaded and a Bad Boss, and she drives her soldiers so hard in pursuit of the heroes across the last book that they end up deserting in droves as soon as they have the opportunity. After Arunis is killed at the end of the third book, she takes over as the most visible threat to the Chathrand and the world in the fourth and final volume.
Magnificent Bastard: Sandor Ott. However much you may think you've figured him out, he's always at least five steps ahead of you.
Comes back to bite him later on, though- the Secret Fist was so dependent on his cunning and charisma to operate that when the Third Sea War comes and he's still away on Chathrand they completely fall apart.
The Woobie: Felthrup. However you feel about rats, you will want to give him a hug every time he appears.
Jerkass Woobie: Taliktrum can be pretty horrible, but it's hard not to feel sorry for him once it's plain how badly he's backed himself into a corner with his people and just wants to be free of the theatrical "prophet" character he's become trapped in. He does manage to find redemption, thoguh.