[SixOfSpades]

First off, we have to assume that it's something on the level of Improved Irenicus we're talking here, because the only thing that the standard Irenicus does well is die. He casts, what, one Mislead before you whack him?

Second, Irenicus's "normal" power level (during the final battle) is difficult to determine....he has absorbed much power from the Tree of Life, true, but Ellesime says that severing his connection will leave him stunned and disoriented, making his hold on that new power very tenuous. This is probably why his Tree of Life is such a pushover. The fact that he's a little bit more respectable in the final battle likely speaks to him recovering some of his poise.

Irenicus does not plan to assume godhood by assuming Bhaal's portfolio--absorbing the Tree of Life is enough to assure celestial status. He and Bodhi are interested in Bhaalspawn simply because, if you're in the market for a couple of souls, why settle for less than the best?

As for Amelysan, though.....she DOES depend mainly on her summons, as Kestrel pointed out. Remove her Slayer Shadows and her Fallen Solar with a Vorpal Bow, and she's just another hacked Cleric/Mage with a cheesy Spear.

I say, the question is this: Could a solo Amelysan beat Improved Irenicus? Answer: NO, thanks to the sheer cheese of Weimer's Shatter Magic. I haven't pried open the spell to see precisely what it does, but from what I've seen, it removes ALL dispellable effects on the targeted creature, lowers the creature's Magic Resistance by 50% for about 1 turn, disrupts any spell currently being cast, and imposes roughly 50% Spellcasting Failure for the same amount of time. Irenicus casts about 3 of these during the first 2 rounds of combat, so unless Amelysan can decoy him into wasting them (and all subsequent ones) on her Summons, and get the Orb of Fear to waste its Anti-Magic Rays in a similar manner, she doesn't stand a ghost of a chance. Barring the even-cheesier Preserving Boots, of course.