I decided to test the potency of combining the Rain spell with Air damage and thought I'd share my experience on the powerful synergy between them.
With a little setup, the combo is incredibly potent.
I was able to solo the entire fight with Dallas/Alexander at level 3 using just Rain and an Air staff.
Essentially any number of enemies of almost any power level can easily be dealt with, even if their Magic Armor is quite high.
The basic idea is that when a puddle is electrified, every character inside will take air damage every round the water remains charged and with every step in it they take. Enemies with no Magic Armor will also become stunned. Once every enemy in the puddle is out of Magic Armor, you've won the fight as they will continue to be stunned until they die (as long as you re-charge the puddle every 2 rounds).
This is a naturally effective combo, but due to a few subtle interactions, it can be much more powerful.
1. Rain is not considered to be an offensive spell, so casting it will not lower attitude or start combat with NPCs. This means it is easy to setup Rain before a fight. Note, this contrasts with almost every other debuff spell. For instance, if you setup oil and an ally walks in it you will lose 20 attitude and they may become hostile, but never with Rain.
Edit: The "friendly" fire slug will become hostile when Rain is cast on it.
2. A wet surface will never naturally expire. When combined with #1, this means you can coat an entire area with Rain before a fight, and because the AoE is so large you can even coat the whole area surrounding enemies without entering combat.
3. Pools are supposed to de-charge after 2 rounds. This means enemies will eventually have a chance to break free. However, when a very large area with numerous enemies is charged a bug will often occur where only part of the area de-charges and the other still-charged part will re-charge the entire thing. This essentially adds an unlimited duration to your stun puddle.
4. Enemies attempting to walk through charged water will take air damage and face a stun status with every step. This means after walking any significant distance enemies will lose all of their magic armor and just sit stunned until their deaths.
5. Due to the damage from #4, AI kicks in and enemies will opt to NOT chase you (to avoid the damage they would take from moving through the pool). However, due to the bug in #3 along with the player re-charging the water, the pool never de-charges and enemies who could have chased down the player or simply walked out of the water will instead stay in place and eventually die.
With rain and air damage, you can weather any storm. Before charging in, paint the area covering and surrounding your opponents with Rain. Enemies will be stunned by your brilliance. It's shockingly easy and effective!