Instructions
Kill the Mage Conster
Take the stairs down to the third level of the Windspear Hills Dungeon after talking to Gerran's child.
Buff up on the stairs and move forward slowly. You will see the mage Conster.
Silence Conster so that you can pull him back to the stairs and kill him without engaging Firkraag.
Loot Conster's body for the key to the cage holding Gerran's child. Go upstairs and free the child, then rest for the big fight against Firkraag.
Killing Firkraag
Buff your party, making sure everyone is protected against evil and fire. Have mages memorize all possible magic missiles and any spells which lower resistance or break protective spells.
Set up traps and area of effect spells like cloudkill near the base of the stairs before you pull Firkraag.
Position your casters off to the sides of the room and have your main tank run Firkraag through traps and the area of effect spells.
Summon monsters and Mordaiken's swords to keep Firkraag distracted so he doesn't attack your mages.
Cast resistance-lowering and dispelling spells on Firkraag first, then kill him with magic missiles.