2 ideas for nightmare to make it less potent.
1. If stun by nightmare, non stun ppl can "wake" affected ppl, be it slapping the face or dunking the head into a bucket of slime.
2. Cooldown flag once big 4 spells are casted. All aggro spells from the flagged caster gets a reduction in casting lvl/effect/duration/save. This would make a robe mage less dangerous in the consecutive rounds from the 1st nightmare/prism/blastwave.
Wouldn't stop alpha fire from 4 to 5 nightmarers (they earned the power), but makes a solo mage less dangerous.