Don't forget that Irenicus didn't do it alone. Bodhi is a very capable ally, and as a vampire has the innate ability to dominate others. No doubt that proved quite handy in taking over Spellhold... she may have dominated key Spellhold insiders some time before the actual assault to help undermine its defenses from within.
Remember Perth the Adept in Brynnlaw? Testing your party seems to have been primarily Bodhi's mission. Perth's "test subject" babbling comments were probably more in line with being under Bodhi's domination than Irenicus's. Now, what happened to the Director ("a bad reaction to a spell" was what Irenicus said if I recall) sounds more like Irenicus's doing.
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->Klutz
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