After completing a boss without taking damage, Tailor will spawn in elevator shafts that you will need to visit and provide materials for him to fix and create the shortcut to that floor.
For the second floor shortcut you need to provide
- 3 Blanks
- 3 Keys and 120 shells
- Master Round 1 (earned by acing the first floor boss)
- 10 Hegemony credits
Materials can be given before they are asked for except for the hegemony credits, which are always last. A good strategy for all of the shortcuts is to tailor a run for such a goal, such as playing the first two floors specifically to stock up on keys and shells.
After completing a shortcut don't forget to stop by Tailor in the breach for your new item/gun. Your reward for this shortcut is the Gunboots.