Good, was just about to start a spell suggestion thread and saw this was created first.
Here's some spell suggestions I was thinking of:
Mass Convert: Casts a convert spell for your element into the opposing element on all enemies. I'd pay a pip for this one. Probably have to introduce it at the higher levels, but it'd be very useful.
Counter attack: Counter attack with remaining pips (even on death). This would be a shield buff that would trigger a counter attack when hit with a spell. I think this would add an interesting tactical dynamic to pvp. I'd probably lower the accuracy of the counterattack though, just so it's not too overpowered and there is risk in using it (you loose all your pips if the counter fails).
Pip destroyer: It'd be interesting to have spells that attack your opponents pips. I can see a whole line of spells along this concept. For example: taking away a pip every turn for three turns, taking away two pips, and taking away everyone's pips (including your own team). The pip costs for these spells would have to be play tested to determine the proper balance.
The main drawback I see for this is that it would possibly make pvp duels much longer. I like the idea though because it's a good counter for those who play defensive and just build up pips for a OTK.
Achilles: This spell would bring up minus 50 percent shields for every element type, but your own. Damage from your own school would be increased 100 percent. Code would have to be put in so that it could not stack with any shield for your own type. That way there is serious risk in using it (your achilles heel).
If people feel this is too powerful, then an alternate version would be to make the 'achilles heel' school type random. So you get protected from all schools but the one random one which gets a boost.