The whole idea of this mod is summarized in its name I guess, since it is all about Redemption of Jon Irenicus, the elven mage who wanted to become a God and doomed himself to eternity by committing a string of unforgivable crimes against both elven society and later many innocent people (your main character included). Still, there were many discussions on the net about Jon, and the possibility of his redemption. I never liked him much, but one day Dave Gaidar suggested a topic in the Attic that captured my imagination. The topic was as you can imagine - Irenicus and the history of his downfall. Sufficient to say that I wrote a lot of fiction about Jon before I came up with the idea for the mod. The text of Redemption was published in the Attic and amazingly - received many warm responses. I ended with ditching all my other responsibilities for three months and coding it into playable mod.
The mod gives you an opportunity upon entering the Throne of Blood to talk Irenicus into siding with you, playing on his sense of wounded pride by reminding him that Melissan goaded him into cooperation. After you defeat all possible and impossible enemies (including some new appearances by old foes) and right before you are to make a final choice about your Bhaal essence Jon will speak to you and request that you keep your word and petition the Seldarine for another trial for him. The result is rather unexpected, and very different from what he hoped for. But I am not going to disclose it here!
Another face (or rather two) to show unexpectedly in this addition is our old friend - the Prince of Demons. Demogorgon gives his little performance and asks you some unexpected questions before engaging in yet another battle. It is possible to humiliate him without actual combat. The puzzles used in this part are shamelessly taken from the books by Raymond Smullyan (Satan, Cantor, and Infinity and The Riddle of Scheherazade), the Demogorgon dual personality is described in the latest Wizards edition of Book of Vile Darkness.