Beating the Archmage in any of the individual ways is extremely cool.
Correctly preparing the Potion of Magical Dissolution and marching right in there to take back the Crown, now useless against the Analander.
Bringing Flanker, who manages to full-on resist the power of the Crown through sheer force of a will thanks to a mixture and vengeance and dedication- a feat seemingly no one else can manage.
Jann's presence preventing the Crown from working altogether, and his tiny pride at finally proving himself.
Leading Aliizi to her fate by taking her to him. The Archmage is so shocked by her seemingly rising from the dead just to confront him that he fails to utilise the Crown and is defeated right away.
Busting open the Cantopani Gate with a spell upon returning to Analand, Crown or no Crown, a great Call-Back to when you began the journey.
Realising who Aliizi really is or will be, the powerful sorceress Bria, and finding out that you've brought her full circle by bringing her to Mampang.
Better still, completely resolving her arc by bringing her briefly back to life by her grave in the Baklands is considered 'the final secret' of the whole series, and not is not only very bittersweet but also revealing of the entire cause of the conflict. The scale of Aliizi's plans and her simple reason (to give her younger self a new life) is impressive.
Aliizi: I still remember waking up in my little hut in the forest and finding you there.... it's like my whole life has been a thread, wound around your finger.
Analander: Please, before you go-
Aliizi: No. I have nothing more to give you. All is done. Do you understand? I told [the Archmage] to take [the Crown] so that you might find me and rescue me... I was only a little girl, terrified and alone. But now... there comes a time where even the greatest of adventures must come to an end.
In 2, if you answer the Impossible Question, and ask to be stronger than anyone ever; Slangg will start turning you to stone. However, by answering the impossible question; you did not convert to his worship. If your Animal Spirit is strong enough; you can pray for help, and this will destroy the temple.
Technically, this shouldn't be possible. It's explicitly stated in the original books that Gods do not interfere in other Gods temples, and even during the sequence you will question whether it would work.
To do this and get the good ending for Cityport of Traps, you'll need to accept Lorag's offer to ZED back in time, as you cannot use Sirisi's answer and get Moulas / Slangg's spell-line in a single game-run.
Infiltrating the Council of Khare by following Flanker's lead and duelling the pair of guards, gaining his approval.
Becomes more of a What the Hell, Hero? moment than an 'awesome' one when Courga counts this as murder in cold blood and calls the Analander out on it.
Saving the Svinn Chief's daughter against all odds right at the end of the first game and briefly becoming the toast of the village.
Killing the Time Serpent, who has a reputation for being impossible to triumph against. Double that if you kill every serpent along the way. Triple if you kill the Time Serpent before talking to Ca-Oth, as part of his spiel he'll start to say that it's impossible; and then realize you did already did it anyways.
Any of the Analander's successful escapes from the hold of Vik's slave ship:
Straight up blowing a hole in the ship and letting all the prisoners out.
Claiming to Vik that they're a friend of his friend and proving it, letting them be released amongst all the gawking prisoners to have an amicable conversation on the deck and then leave on a smaller boat.
Best of all, starting a massive successful revolt, joining the fight to remove Vik's crew and then leaving the ship to be Captained by your friend Tomas as you escape for good.
Using your spells to mimic being an extremely powerful sorcerer and occasionally scaring people senseless, probably the best occasions being when you can pretend to be the Archmage himself with GOD while in Mampang.