[Eerhardt]

Before I open the door Irenicus comes through (check your final save), I cast protection from evil 10' radius (lasts pretty long if your priest is of high enough level). Then I open the door and as soon as Irenicus has summoned the other demons I run for the stairs at the bottom of the screen. I have Jaheira cast Defensive Harmony (she can cast it pretty fast) when she's at the bottom of the screen and put Minsc and my fighter in front of my party on the stairs to make a stand. I use Aerie to improve haste them and because of Strength bonuses (Girdles/Crom Faer) my fighters make short work of the demons. I apply healing if needed since Irenicus didn't bother to come after me yet. He probably cast Mislead so I buff up my party and have my fighter go after the Mislead Irenicus, who he pretty soon dispatches. Then it's just a matter of stamina; I keep bashing on the real Irenicus with my entire party (preferably melee) and drink potions when needed or cast breach if he has any protections on him. It's a tough fight, but eventually he'll loose.