Some insight on how I characterized Halaster now that I've played him in front of my players. I get way into the roleplay aspect of D&D but I play my characters a bit strangely. I've always done this, I get a general idea of what the character is like and then wait for things to happen to them. Once something happens to them I determine how they would react to that, like watching it happen to them and reporting on what they do. Sometimes you have no control over your own NPCs, and Halaster is no different. I obviously control what they do but sometimes it feels like writing up an incident report rather than playing them. I'll paint some word pictures of what I mean in italics.
You hear muttering with no discernable source. "Damn kids and their vandalism. No respect for a good dungeon wall." As you watch the gash in the wall, there to mark your path, fills in with smooth stone until it's like it was never there at all. Then, right as the golem rears up to attack again, you hear a scream of panic and in front of where the gash once was appears an old man with wild red eyes, even wilder white hair and a thick beard of the same color. He wears a robe covered with stitched eyes and mouths of all shapes and sizes. He points a finger pulsing with necrotic energy at the flesh golem.
In his regional effects on Undermountain is the ability to create a potentially infinite number of scrying sensors in the form of a 1 foot diameter ghostly floating humanoid eye surrounded by notes of light. At any time. He sees through these sensors as if he were in their spaces simultaneously and he can orient them in any direction, though they're stationary. And he wears a Robe of Eyes that allows him to see in 360 degrees around him so Halaster's attention is constantly quite split.
"Child, I have guests all over this maze. If I were to speak to them all I'd never get anything done. And I'm a very busy man. Things to learn, experiments to maintain. At this moment my attention is so split I may just go mad." He laughs for an uncomfortably long amount of time.
Second important thing! Halaster's Intelligence score is 24. For reference, the average is 10 and the highest adventurers, extraordinary people, can get without magic is 20. Cha boy is smart. Meaning all of my D&D knowledge is useful for things! I can name drop D&D monsters and lore and have it mean something! Which is exactly what I did, like when a party member was sad about the death of the flesh golem they were trying to calm down.
Halaster raises an eyebrow, "Attachment was your first mistake. A flesh golem is nothing more than an elemental spirit bound to a stitched mound of flesh. It must be overjoyed to be free, if it even remembers its imprisonment at all."
Third! He's self aware, but only a little bit. He's aware that the Knot in the Weave is what resurrects him and that it can cause madness, obsession, amplification of ambitions, and he knows he can never escape, so he figures he may as well have fun. Learn. Become the greatest wizard ever to live. He knows what happens in his dungeon always leads to destruction and most importantly he knows everyone is there by choice, by obsession with either the dungeon itself or something in it. (I noticed a theme with many NPCs and decided to make it an actual effect of the Knot in the Weave.)
When one party member sassed Halaster another tried to make up for it by saying if they had a choice that member wouldn't be here. He has reason to keep them together, because together they will clear out many of his problems and give him a show in the process. In response to saying the sassy member wouldn't be there if they had a choice, Halaster had this to say.
Halaster smiles, "If you had a choice? Of course you had a choice. If you didn't you wouldn't be here. Everyone is here by their own choice, myself included. Undermountain calls to us all, but we all choose to answer. You're all still together by choice or you'd already have been ripped apart."
And finally, his 24 intelligence means he interrupts himself a lot. Multiple trains of thought, thinking about what to replace old traps and monsters with, what new experiments to perform, where to check on next. All while meeting his newest guests face to face.
And of course, he doesn't want to spoil the spirit of the dungeon. I'll just copy his last line to the heroes wholesale, coming right after being asked where the stairs to the second floor are, which he of course knows.
Halaster doesn't directly turn his head to look at you but several of the eyes on his cloak turn to face you. "Wouldn't that spoil the surprise? Where's the tension, the drama, in the architect simply telling you the answer to the puzzle? And even if I were to tell you, would you believe a mad old man?"
He walks toward the center of the room, "A trap is useless once it's been sprung. I Wish this mess would just get itself gone." As you watch, the shattered crystal orb and wyvern bones just disappear. He continues walking toward the northernmost door, through where the debris used to be. "Now what to replace this with, was the dragon-kin a good idea? Or something more elemental? Perhaps undead was the right way to go, if Nester weren't a cackling pile of bones perhaps he'd have some input."
He interrupts himself again, waving his hand over his shoulder, the eyes in his cloak swirling about, "We will see each other again, children. Though I will see you long before you see me. I see all under the mountain. Rest well!" As he approaches the door it momentarily opens before him into a glowing gateway, then closes again once he passes through. He leaves you alone.
Why yes, Halaster did use the most powerful spell a mortal can cast, Wish, to clean up a mess on the floor. And that's how I play him, really. So powerful that he has nothing to fear, even if he could die to begin with, but the Knot in the Weave won't allow that. The Mad Mage must live on. And he will learn on until he knows all, then he'll make more things to learn.
(This was absolutely an excuse to show you some of my favorite lines from the Mad Mage but hey, maybe you'll find it useful. Maybe I'll post more of the Mage's ramblings here if you like these? Happy dungeon delving!)