Sign of Chaos by Roger Zelazny

 Merlin manages to escape from the hallucinogenic world created by Luke, using the Vorpal Blade to get by the Jabberwock (yes, Zelazny steals from Carrol here), though it helps when a Fire Angel (chaos creature) shows up on his trail and the two beasts fight one another. He contacts his aunt Fiona and his older brother, Mandor, and Trumps away from it all. 

Returning to Amber, Merlin works out a way to free Luke's mother, Jasra, from the coat rack curse, and makes plans to use her freedom as a bargaining chip when Luke finally recovers from his far-out trip. A delegate from the kingdom of Begma arrives in town with his daughters, and he is importuned into entertaining one of them, Coral, showing her around town at first. She expresses a desire to see the famous Pattern of Amber, and surprises Merlin by stepping onto the Pattern and walking it successfully. It turns out that Oberon had an affair with her mother, and she (like so many others) bears the bastard blood of Amber in her veins. She uses the Pattern to transport herself elsewhere, leaving Merlin in a bit of a quandry as to what to tell her father.

Zelazny begins to play around with the question here, "What if the Pattern is actually sentient, not just an artifact as we thought in the first five books in the series?" This, of course, leads to some very strange happenings as we progress.

Later, Coral's sister Nayda approaches Merlin, ostensibly to find out what's become of her sister, but it becomes apparent quite soon that she has some other motives, far deeper. When Mandor meets Nayda, he recognizes her as being possessed by a ti'yiga, a chaos demon which can take over human's bodies for a time, and we finally get to know what's been going on with Merlin's odd encounters with people who know far more about his business than they should, and who seem to have a strong urge to protect him from danger. When he checks up on them later, they've usually suffered a form of amnesia covering the time of the encounter. Someone has placed a geas on the ti'yiga to watch over Merlin, and it's been tracking him through Shadow ever since.

The mercenary Dalt appears on the scene and demands that Luke and Jasra be surrendered to him. To avoid a battle between Benedict's forces and Dalt's, Luke challenges Dalt to hand-to-hand combat, with the loser to become the prisoner of the winner. Dalt wins, and disappears with Luke for parts unknown. After that, Merlin frees Jasra and works out an alliance with her to assault the Keep of Four Worlds, freeing it from Mask's domination - at the end learning the identity of Mask and also of another source of some clumsy attacks on his person.

Good fun, still twisty.