There is one core ability per class that should be kept from the old KMOD: the fighter's berserking, the mage's mana creation spell and the cleric's healing spell.

They should now all work more like berserking, i.e. the higher the amount of SP you wait to be collected, the stronger the effect unleashed: just as the fighter gets a higher speed and damage boost that lasts longer, the mage creates higher amounts of mana and more colors if the SP counter is higher. The cleric's heals also get stronger.

Maximum SP depends on Intelligence, SP regeneration rate on Wisdom. Basically, putting points into INT allows you to reach the higher tiers of the class spell (e.g. for mage tier one creates only blue mana, tier two creates blue and green mana, tier three creates all three colors at once), whereas putting points into WIS allows you to use the ability more often at full charge.

p.s. In cooperative, it might be interesting for the effects to apply to all players.