Maybe it could be some sort of leadership class, with bonuses to other people, not quite sure how to do it without making things more complicated, maybe make it universal, for 12 PP everyone gets an extra AP per round, or die at -1 HP, or damage, probably as a percentage. That way you could set up a set of altered stats for everyone at the start of the round but not need to go back to the old stats until the leader died...
As for bonuses, give them low-cost and some penalties to attacking, maybe throw in a couple of AP points or a discount at the shops, you could even give it positive PP so it would be like a flaw.
*Psies* Ummmm, maybe they could start with a basic telekinetic attack, maybe 6AP to deal 1 damage to any point on the map, no crits, no misses. They could generate shields to deflect attacks, disrupt the actions of intelligent opponents, such as bandits and spellcasters, they could probably take perks to improve their TK attack(maybe by studying anatomy), maybe even project a shield onto another character or hold back an opponent through brute force. As for flaws, a weak mind would need a couple of AP to recover from Psi actions. Excessive psi usage might cause some people to become mentally unstable, probably losing actions or wandering randomly, so, maybe a limit on the number of psi actions per round. Psi could be about having a small number of actions that you improve while magic might have more actions with no ability to upgrade them.
Cheaper spells might be less powerful for the actions but use less actions, so they retain some utility in efficiency. They would probably have a basic single target attack, something with a radius, a more powerful single attack, something to slow enemies, maybe a spell to increase people's damage. You could give them an elemental motif, lob a rock for a cheap attack, a bolt of lightning to affect an area, and a stream of fire to mess up one big target. Lets say lob a rock for 2 AP and .5 damage, lightning from the sky for 6 AP and 1 damage in a 2x2 square, and a fire stream for 8 AP and 4 damage. Hmmm, probably a little more damage than that but mages can choose their weapons freely and have some utility abilities, so they really shouldn't deal as much damage as other classes.
conjure mud under someone to halve their movement for 4AP, make an earthen barrier with 1 HP for 3 AP, use electricity to stun an adjacent opponent, costing both of you 6 AP, heat up a weapon increasing its AP usage by 50% for 4AP, I don't know, this is just an example of how it might play out.
How would you feel about having a second HP meter for mental or magical energy? people could have a limited amount of magic for each scenario, but I am not sure it would add anything and would be a mild hassle to track...
This is more about the basic principals than any specific suggestions...