Name: Mind Crush
Circles: Water / Mentalism
Description: Affected unit suffers moderate illusory damage and has -4 to its spellcasting ability scores for each casting of this spell. Will save negates both damage and penalty.

Notes: I asked Aaron how stats worked in relation to spellcasting and he said that reducing a spellcasting ability reduces both available mana and damage. If ability scores work as in DnD it loses 1 damage for every 2 points of ability lost. Effect stacks so if you want to floor unit's spell damage cast it multiple times. Illusion immunity protects against both effects. Damage is phantasmal in nature so illusion immunity protects against it. Save negates damage as unit realizes it's just an illusion.

This spell works for me. Although I think it might be a specialty spell - I guess it depends on how things shake out.