Effects of overusing Soul Caster
Looking for some advice and one of my players in an upcoming Cosmere game is really interested in having an effect be part of their backstory and i can't find this lore anywhere.
To Sum up: my player is remembering somewhere in the lore that if one uses a soul caster over and over the person will slowly turn into the material they are casting. (Specifically they remember someone turning into Smoke and someone else turning into grain?)
They want to make their PC an artefabrian and specifically their reason for adventuring and researching soul casters is that their childhood friend is slowly dying (or has already died) and they want to find out how it happened and stop it from happening again.
I will be running Stonewalkers and while we don't need to resolve their goal completely i am perfectly happy to weave it into the story and have them make progress in that research while they play the campaign. EXCEPT. i cannot find lore, background, info, or anything regarding this outcome for using soul casters anywhere.
We are a group trying to stick to the lore fairly closely and i don't want to just make something up with no basis in the written books. I can't find this and am hoping someone else can point me to the page and book so i have something to go off of before i try and invent rules and characters into the story for them.