From the movie "the FOG"
http://en.wikipedia.org/wiki/The_Fog
WATER and AIR
You could use the Eater of the Dead as a basis.
Or better yet the Ghost Ship Armada so that it only attacks coastlines.
http://dom3.servegame.com/wiki/Ghost_Ship_Armada
http://dom3.servegame.com/wiki/Damned_Admiral
--------------------
Question: have you created a list of such spells already in place. Im all for such mods and will definitely follow this one. But I like it even better if they try to fill gaps. I dont want to suggest in areas that are already loaded with cross-magic summons