"Not that it's not lovely for the right sort of occupant but yeah nah. Changes to myself like what?"

Natives of certain realms have curious properties. Given an example, you could shape your essence to use foreign abilities. Or accomplish other goals - some planes' denizens keep their souls outside their bodies in various forms, which you could also do. Pause. I do not recommend it. It would be hazardous in your current line of work.

"More so than keeping it in my body? Because that's already gotten me killed a few times."

The vague mental impression of a shrug. It is not without its advantages. But if you choose to do so, ensure that no one touches your soul while it is vulnerable. The consequences are dire, by all accounts. 

"Noted. So we just, what, walk up to Mephistopholes and tell him to fuck off, is this an exact words kind of deal, does he get a will save?"

Faint amusement. We are well beyond the realm of will saves. When you invoke a True Name, the effect is either within your power or outside it. Nothing more, nothing less. And you needn't worry about the exact words. He will know your meaning.

"What does quashing his essence mean?"

He would cease to be a part of the universe. Kill him, and he will reform in his palace in Mephistar. Quash his essence, and he will be gone forever, and a blow struck against Hell in the balance of Good and Evil.

"Gosh. Uh, in what ways am I more powerful now, like, am I just higher level and it merely feels weird to do that all at once, or...?"

You are higher level, as you say. You also have access to abilities in keeping with your new power - abilities which your home planet has never heard of, though this one has a handful of legendary heroes who have possessed them.

"Could you be more specific."

You could alter your magical channels so that you no longer need to speak or move in order to use magic. You could enhance spells above the ninth circle. You could learn the secrets of certain spells which are inherently beyond the ninth circle. You could - ah, your magic has already adapted to one such enhancement. You will find that where your spells needed the energy and structure of diamonds, before, and other such sacrificial materials, you may substitute your own power. Only to a limited extent; it will not afford you a free Wish, but it will allow... three Limited Wishes with a bit left over, per day. It is possible you could increase this limit, through practice and experience.

"...wow."

I do not give this power lightly. You bear the weight of destiny upon you, Truthseeker. I know you will do what must be done.

"Thank you."

Is there anything else you wish to ask?

"...Deekin wondering if Knower want to be not in glacier anymore?"

Another faint impression of a smile. My prison fits me well, singer. Do not trouble yourself.

"Well, if you're sure."

"Oh, while we're here, can you tell us the name of the Sleeping Man's True Love, the one he's waiting for? It seems like the kind of thing he might like to know. - not her True Name, just, uh, her name name."

She is the one you call Aribeth de Tylmarande.

"Huh. Alright."

"Do true names tend to stay the same forever? Like, presumably the descriptors are not all true at birth."

No, they change over time. But if you know a being's true name, you know their true name.

"Huh. So we'll get an update if Mephistopholes settles down and takes up spinning?"