The finishing blow against the Balor. So the legendary weapon that is needed to kill it was lost. Game over right? Wrong. The Fateless One pins down the Balor with its own Fate, then recreates the legendary spear using Fate itself and hurls it right into the Balor's eye.
The ending to the Warsworn quest-line. The ancient Niskaru Lord Khamazandu is about to be released from its prison, hundreds of cultists guard the mountain, Niskaru are blocking every path, hungry for blood. The Fateless One arrives at the head of a four man assault team wielding the reforged hammer which drove the Niskaru to imprisonment to begin with. A violent rampage follows, ending with a You Shall Not Pass by the group as the Fateless One proceeds to single handedly fight the leaders of the cult and re-imprison the Khamazandu.
Fomorous Hugues at the Well of Souls. A half-pint scientist is the last person you'd expect to drop a Tuatha soldier, but he succeeds and draws the rest away from the Fateless One. It's easy to cheer the guy on and insistently believe he'll survive despite Agarth's predictions. And simply by meeting you, he does!