[andrewas]

You should be able to take down the demons easily enough at those levels. Do so, then run like hell. Its possible to get out of irenicus's LOS, and then all you have to do is wait for his defenses to wear off. Unfotunately, irenicus slayer change dosent have the side effects yours does, so you'll have to take him down in that form.

If you going to summon anything in this fight, make it something tough. Mordenkainens swords, spring to mind, as do skeleton warriors. Probably wont last long, but every hit helps.