My tactic:
Summon a Fiend. When you are casting it, open the final eye so irenicus somes out. the demon shold be ready when the battle begins. Now retreat with all your charcters to the souh. This will draw Irenicus demon to you, so you can concentrate on slaying them...
revive any killed characters when defeated them. Cast Pierce Magic/Shield, Breach lower resistance and so on Irenicus (the real, better use a True Sight first).
Then, it is Elementals and whatever you can tink of that goes!
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We call him Bobby Corwen
