Quote Originally Posted by Elves View Post
For casual creatures that don't need to be uber-optimized to a stitch, I honestly enjoy the SLA metamagic feats. IIRC pit fiends have quicken SLA on fireball, but you're better off putting it on their teleport or dispel. Give Quicken SLA to the devils they summon as well, and you've got a much better action economy.

If you want this encounter to actually be challenging at that level, even to a lower-op party, add more monsters or have the confrontation come after a big encounter that tempts the PCs to use their big stuff.

What are your players' usual tactics?
Ranger: Attack with arrows
Cleric: Spells and close combat
Rogue: Close Combat and Sneak Attack
Wizard (Conjurer): Summon monsters and spells
Paladin: Close combat and spellls
Bard: Spells