[Endoperez]

I think Cloud spells are possible. I don't remember the details, but increasing some feature by 3000 nade a cloud that stays in place for 3 turns. IIRC, this was used in the mod that fixed Mists of Deception.

I've always wanted to see more cross-path Water spells. Poor Masters of the Way...

Water/Death:
* Streams of Tartarus: chilly waters of tartarus cause various nasty effects to living beings
* Death/Water ritual: Call Ghost Ship, including a commander with Sailing ability (use sprites from Damned Admiral spell and perhaps some mercs). Could also work as an underwater combat summon that summons lots of undead that disappear after battle.

Water/Nature (existing spells: naiads, bone melter, Mossbody):
* low-level version of Bone Melter
* underwater spell (or several) that create an AoE poison cloud effect
* W1N1, 100 fatigue (1 gem) combat summon that calls 2 Naiad Warriors

Water/Earth: Earth Grip/Meld-like effect with high AoE (transforms the battlefield into mud).

Water/Astral:
* Waterway, a teleport spell restricted to seas and coastal provinces (hard to do or even impossible).