“ In one region of a forest, all of the trees are identical, down to the leaves and the twigs. If the PCs carve something into one of the trees, it could mystically propigate until it covered all of the trees, or could vanish since it was not carved into the one true tree.”
“ Magical Fiends: When a mage or wizard casts a spell and draws more energy than s/he needs Magical Fiends are drawn to that spot and they feed of the extra magic as long as they can. When someone's magic is being fed off of they can't cast spells as well and they feel weaker. The only way to remove a magicial fiend is for it to be drawn away by someone else's power or to go to the very spot you first cast the spell and kill them”
“ 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.”