The final battle in the second volume. After losing thousands in a desert, they begin a long siege of a large Fanim city. A plague epidemic breaks out in their camp, and hundreds die every night. Finally, they break into the city and sack it - only to find themselves besieged inside the sacked city by a Fanim army ten times larger than their own. Starvation begins afflicting them. After they crucify Kellhus, who shows them he truly is a Prophet by pulling out his own heart, they repent. The day after, the poor starved remnants of the Holy War march out of the city gates and charge the besieging Fanim. And they win.
In The Judging Eye, when Mimara banishes the Wight-in-the-Mountain and shuts the gates to the afterlife.
The final scene of The Thousandfold Thought, which doubles as a Tear Jerker.
Almost any time Achamian gets to demonstrate why the Gnosis is so respected. For example, attacking a group of Imperial Saik sorcerers and their Grandmaster, killing all of them single-handed, and then fighting off the most powerful demon Iyokus could send after him.
Achamian and Cleric defeating the Father of Dragons in The White-Luck Warrior.