I cannot seem to find the actual Pariah game link any more?
Viewing post in Complete PARIAH sandbox (zini selection) comments
I removed the game from public access because it has been superseded by this one! The Complete Pariah Sandbox contains all the material you need to run a game of Pariah. It is very much a work in progress, but I wanted to be clear that this replaces rather than augments PARIAH Volume 1.
If you previously bought or downloaded Pariah on itch then you can still access the game through https://itch.io/my-purchases. What's more, a reduced price PoD edition of Volume 1 is still available on Drive Thru RPG if you don't already own the original and would like to.
I think making the Other Realms fit the themes of your game is a good start. If you're doing Anglo Saxons vs. druids then maybe fitting it to the celtic pantheon could be cool. Think of realms like domains or schools of magic in 5e if it helps,
Otherwise, if it's the improvised magic or the connection to hit dice that isn't landing for you, the system from which it's derived is worth a look:
https://slightadjustments.blogspot.com/p/glog-magic-dice-primer.html
The system was the invention of Arnold Kemp but I think Spwack's version (above) is pretty neat.
But I may have gone off the rails a bit there. Is there anything specific I can help you with?