Wizardry: Labyrinth of Lost Souls

Story-related. Can be missed if you make the wrong choices.

On the final quest of the main storyline [Rescue King Diement V] you'll come to a point where you talk to Gregor on B7F of Shiin's Dungeon (X:18, Y:16) after fighting the Hydra.  If you choose to believe him you will end the game after a fight against Shiin, if you choose not to believe him you will fight the Ala Cabra, netting you this trophy.

For more information on the quests you need to do and coordinates see Savior of the Empire.