“ God has been slayed by a mortal man and his head is now worshipped and put on a pedestal. The PCs are hired to steal the head and bring it to a mystic that claims to have the power to revive God.”
“ Elves use nature as strength and borrow from the trees to keep them living. An elf out of the forest for more than a day begins to die and within 3 days is dead without borrowing the strength of nature.”
“ When you sleep, your soul briefly returns to the place where it was created/goes to when it dies, and seeks nourishment. Everybody's soul is created with a little link (or you could say a greater entity calls it back) to that place so that it can return easily, but upon death, the soul returns via that and annihilates the link as if returns.
Also, as an added thingy, you could say the entity supplying the link, or residue of the links themselves, (whichever) is the source of all arcane power.”