“ With a huge number of sacrificial victims, another realm long ago secretly bound a Prince of the land spirits, Iorstonn by name, thus ensuring the fertility, and improving the magical defences, of their realm. But binding that Prince to one spot has disrupted the weather and magical patterns (ley lines?) over half the continent. Things have become bad enough that a coalition has been formed to rectify the situation, once divinations have established the cause.
Your party is one of the teams assembled to do the rectification: find the binding object and steal it ('so that we can destroy it here in our realm, of course'...*) or destroy it over there. Presumably the Prince will be grateful to his rescuers and angry at the binders, but with a greater spirit like Iorstonn one can never be sure: such beings are 'tricksy'.
* Of course, the rulers of our realm might want to control Iorstonn for their own ends...”
“ Arkths or Ravagers: These are large landbound crablike creatures about the size of Grizzly Bears. They live partially in the astreal plane. Their food is magic. They can sense it at huge distances. Since spells and such are hard to eat (being in motion) and magical places are the equivalent of a sea of krill to them, they are looking for magic stashed in concrete places. Their primary food source is magic items, alchemical potions, and enchantments. They do a pretty good job of mangling/ eating the physical aspect of said items in the process of chowing down. These things will be the bane of dungeons everywhere, as they will slowly eat away much of the treasure (and the magical traps... so it can be advantagous to follow these things). Note: They will attack people with highly magical natures (i.e. high magic powers). They will probably kill the person in the process of sucking out the power.”