Armour set: mainly crimson(different legs?)
For the challenge you would have to keep his weapon nomal/raw but you can use pine resin, only after using an Estus though(bushido blade attack)
For magic you can only use throwing pyromancies(firaga) and lightning spear.
I haven't considered what SL you would need for this build but presume minimum SL necessary. I might introduce a stage system(can't use certain magic before O&S etc.)
There's probably some detail I missed when trying to make this class so feel free to suggest changes.
Another character would be kain(FFIV) which would be ornstein gear in ng+ with similar magic ability.
I'm very interested to see what other character classes you can come up with