...Okay, fluffs are whatever you can come up with. That thing is all on you.
But system-wise, maybe you can take a look at
Unknown Armies 2e for an alternative. (Actually I still think UA2e is one of the top-10 system I've ever seen and the only lite-type I could tolerate. Didn't read 3e though.)
The Mages/Adepts in UA are mostly edicts-based, in that they don't do MPs or per day spells, but "exchanges" in form of "charges".
Spells have three levels, where the cost is equal to the power:
Minor, you trade with minor inconveniences.
Significant, you put out meaningful efforts and actions.
Major, you do something that's once-in-history, or give up something life-changing and usually permanent.
For examples,
劇透 - :
A Bibliomancer whose source of powers are hoarding more and more books, his requirement would be having a huge (thousands and above) personal paper library, gets depowered if he damaged or destroyed any books, and his Mi/Si/Ma would be:
Gather a new specific collection that's worth $100+/Read through another copy of the same book like a CCTV, or Find out what would happen to a topic in the next 24 hrs.
Gather a new rare $500+ book/Find out every written info on a living target, or Make someone no longer able to read/write/speak/listen/use any languages at all.
Gather a unique priceless-level book./Obscure any fact from the world or rewrite every single copies of a book as desired.
Or, pornomancer, whose power comes from one specific porn actress's videos, his requirement is that he has to exactly duplicate specific sex scenes of the "Naked Goddess" and gets depowered if he didn't, and his Mi/Si/Ma are:
"Do it" that specific way consensually for at least one hour/Target can only choose to speak the truth or not at all, or make people who wants to attack you risk their psyche to do so.
"Do it" that specific way with people who resembles the actors in the scene and locations that resembles the set/Make any successful roll you see with your own eyes a failure, or makes you go to where you "should be" wherever it is.
Exactly Re-enacts a part of the life of the "Naked Goddess" not on video, that no one had ever done so before/ Undo any spell, or Makes you top-level famous globally.
you can see its structure is composed of "Restrictions-Taboos-Trades".
If you read the old-style 仙俠 as well as actual Taoist practices, its that they really need to
give-up and follow so many rules to get to where they are and to stay where they are, but in exchange it gives them power that're beyond human, that isn't just about how much damage you can do when you fly around and cut people.
How to make that a meaningful part of your mechanics though is a bit of a problem.
