[Cerek the Barbaric]

I don't know what Difficulty setting you plan to use, Pyrenk, but I defeated Improved Illyich 2.0 with my solo Skald - and didn't even use the Acorns until the very last part of the battle with the Glabrezu.

That was on Normal Difficulty, but if I could beat Improved Illyich in my first ever solo attempt with a class I've never played before, surely a more veteran player that decides to take along some party members would have an even easier time of it.