Trigger Witch (EU)

Story-related and cannot be missed.

You will fight the Man in Black at the end of the dungeon at the Varrian Ruins. It's a four-stage boss fight.

GLITCH WARNING: If you die during the first two stages, there is a chance that you will respawn in the starting area and will be unable to leave it.  Close out of the game and relaunch it and that should take care of the problem.

The first two stages, the Man in Black will be surrounded by a force field, making him difficult to hit. You need to shoot near where his own bullets are coming out in order to hit him. I suggest kicking the difficulty down to Very Easy and just wailing away, taking the damage instead of spending most of your time attempting to dodge his shots. You can also kill the spawning rats near him to deal poison damage - this may be the intended method of defeating him.

The third stage takes place during a broom flight section, while chasing after the man's rocket.  You need to go through a few rounds of defeating the Man in Black's cannons, then shoot a few shots into the rocket.  Once you've finished this phase, there will be a good amount of time where you can still control the broom but it seems like nothing is happening; just wait, eventually the cutscene will kick in and the game will progress.

The fourth and final stage is another gun fight. This time, you can only damage the man during certain times of the fight - the two I found were after he does a drop attack and when he's firing rockets from his back. Just keep shooting.  Make your life a bit easier by taking out the gun and electricity turrets when they appear on the ground.

The trophy will unlock during the cutscene following the fourth stage of the fight.