I'm not sure if it'd be possible, but spells that effect huge areas of the map could be an interesting feature. Unlike normal spells, such an ability would be using the world map for it's targetting. Extreme high level spells for those truly terrifying higher levels. Being once the God-King of the Dreamworld and tore the veil between realms to invade the mortal world, such would possibly be not too far-fetched.
Example possible abilities:
Impatient Dead: Reviving all corpses on a section of the map.
Divine Light: Damage all undead in an area of the map.
Great Blaze: Set everything flammable in an area of the map on fire.
Blighted Land: The dead will always respawn in this land. This does not mean they're your friends though. Turns bodies of water into swamp water, normal grass into dirt.
Cursed Blood: Causes fumes to appear from all the blood in an area, making pools of poison water damaging anyone near/in them.
Foggy Mists: Creates fog that makes it harder for anyone to see through. Increases stealth and lowers vision radius for AI/(Player?).
Storm Clouds: Just makes it rain. Maybe strike thunder occasionally.
How it could be balanced out is depending on the ability, it could require different magical regements. Setting up a ritual area for it, with it only having a limited range depending on the spell.
Inspired by this video.