man your on a roll, this idea is also really cool. of course it would need a lot of fine tuning but the idea is great.
Wind World Spells:
Lore of fire: turn x% of mountains into volcanoes, all surrounding improvements and units are killed/destroyed, cities next to volcanoes get halved populations and some buildings destroyed.
Lore of metal: spawns a mineral resource on most mines in your empire. spawns some minerals on peaks in your empire.
Lore of Shadows: permentantly allows Hidden nationality toggling on all your units.
Lore of Death: reduces the population of all cities on the map by x. deals death damage to all units in the world bar your own.
Lore of Life: gives all your units the 'immortality' promotion (ala blood of the phoenix).
Lore of Beasts: converts x% of barbarian animals to your team all animals get heroic strength 1 and 2, and heroic defence 1 and 2.
Lore of Light: removes all fog of war (not the real black unexplored stuff, just the stuff youve already explored.)
Lore of the Heavens: causes comet of cassandora tokens (not yet implemented) to be placed randomly all over the map. (even in your borders)
Elemental World Spells:
Fire: slowly starts turning all plains to desert, all grasslands to plains, all tundra to grass and all ice to tundra. starts forest fires all over the map. (use end of winter map script)
Water: turn all land tiles adjacent to water, that does not contain a city, to coast.
Earth: Turns x% of the map to hills, (lower peaks, raise flatlands.)
Air: deal lightning damage to all enemy units, create rainstome improvements randomly all over the map.
ice: trigger 'end of winter' effect but in reverse.
Racial World Spells:
Lore of Athel Loren: turns all tiles in your empire to ancient forest (except peaks), turns desert and tundra to plains.
High Magic: increases miscast chance of all spellcasters except your own by 20% for the remainder of the game.
Dark Magic: all enemy units to enter your borders have a chance of getting the 'Unbearable pain' promotion. all your spellcasters get +1 unholy strength, +1 death strength.
Lore of Day: removes invisibility and hidden nationality from every unit on the map, demons get permanent -20% strength.
Lore of night: all your units gain Invisibility and ignore borders.
Magic of the Horned Rat: starts a plague ala Rhyes and fall of civ in all enemy cities.
Necromancy: every living unit that dies from now on is ressurected in your capital asa skelleton.
Nurgle: all rival units get the diseased or plagued promotion
Tzeentch: x% of units get the mutated promotion
Slaanesh: x% of units in your line of sight are converted to your side.
Ok, thats the end of my crazyness

i know theyre all EXREMELY insanely overpowered, but thats just random ideas.
