1. Go to Doom North first (you must have your own key, otherwise you can't get in alone, and you need a key in FB).

2. Pay attention to avoid patrol after entering. There is a slope in front of the left. Here, grasp the angle and jump to the handrail of the left stairs. Don't fall! ! !

3. Then walk against the wall. There's a door on the left that can be opened with a key, and then it's OK.

This method is not necessarily only applicable to the mage, but also my MS number can be input in this way.

It's not difficult.