If you happened to miss the Elemental Spell Contest, (like I did), and want to get some ideas out:
Eruption - Small volcano appears on battle field, spews lava randomly each round within area of effect
Chain Lightning - Lightning spell which affects multiple targets. Standard spell but - increasingly effective against heavier armour. (heavy plate having more steel than light plate). Less effective against padded and leather. Intelligence determines number of targets.
Summon River - Calls a fast moving stream to cross the battle field. If any units are in its path they have a chance of being swept away. (removed from battle but still on the strategic map). Stream remains on tactical map for the remainder of the battle, it is safe to cross but units within it suffer penalties.
Spell Mirror - Single use, target unit will reflect any spell that is cast on it, back at the caster.
Dispel Magic - Attempts to remove a negative effect from a friendly unit, or a beneficial effect from an enemy.
Will-o-wisp - An extremely hard to hit creature is summoned that floats around the battle field randomly stealing experience from units! If the will-o-wisp is killed all stolen experience is granted to the unit that killed it. If the battle ends and wisp is not killed, all stolen experience is lost.
Duplicity - Creates duplicates of target friendly unit which are scattered around the tactical map. Original target is placed randomly amongst them. Clones cannot attack but move randomly. Clones disappear if they receive any amount of damage. If the real unit attacks or recieves damage, all the clones disappear.
Mind Control - Based on the intelligence of the caster, he may possess an enemy unit of given strength and decide its moves for the duration of the spell. Caster forfeits all other actions however.
Animate Dead - Target fallen unit is brough back to life as an undead version of itself! If killed again cannot be brought back again. Effect only lasts for duration of battle.
Resurrect - High cost mana spell that actually brings a unit back to life, the effect is permanent even after the battle is over.
Chaos Bloom - Radically alters the tactical map, creates many obstacles and terrain elevantions, even hazards. Almost a maze-like effect as end result.
These are all tactical spells. I tried to include only the more interesting ones. Feel free to dismantle/modify/completely disregard.
