As part of Anwyn, one of the things I was planning was to have some unusual effects happen in Tuist Rhion because of the high concentration of magic in that region.
While watching a recent vid, the creator of a setting called Final Age, talked about something he named Ghost Storms (which create/summon undead of various types) which happen if there is too much magic use, and that got me thinking about how the Bladelands setting (a continent on Shadow World) had Bladestorms, and the rest of Shadow World had flow storms.... and thus I was inspired.....
And since I was already going to have Tuist Rhion be highly magical, I got to thinking that something similar could happen in Anwyn as well....
And what we have are the Wyrstorms (pronounced: WEER storms). I am still working out the details, but in short, they are filled with red and green lightning, they last anywhere from 20 minutes to 2 hours (20 + (2d10 x 5) minutes). And during a Wyrstorm, random portals to other worlds and planes can open, pulling almost anything through. If a Wyrstorm happens in the presence of a portal, like those found in the Esker Highlands, those portals will automatically activate.
so the mechanics I have worked out so far look like this......
1) Anytime a spell is cast, if the dice roll is double sixes, then the GM checks for a Wyrstorm
2) The GM rolls 2d10 (open-ended), and adds in the Tier of the spell. If the result is 20 or higher, a storm forms over the course of the next 2d10 minutes., the area covered by the Wyrstorm is 1-10 mile radius
3) The more magic items you have or active magic going, the more likely you are to attract lightning strikes (which otherwise happen randomly -- I need to work up a table of possible effects. there will be chances that the party takes a lightning strike or that a creature of some sort is portaled in
4) After the storm is over, all spells receive a -4 to casting for 24 hours and any magic items may also have been altered (either weakened or made stronger a 2d20 roll for each item, 2-5 = item weakened or perhaps made non-magical; 17-20 item made more powerful; 6-16 = odd: item drained for 24 hours, even: no effect
In the cities, they have created Storm Rods for these storms to redirect any lightning strikes into the ground - just a long metal pole with a crystal at the top, that is stuck in the ground - cheap and easy to make, but every town and village has them....