This is almost like the fly glitch instead you dont stay in the air and go really fast.
You need 2 people.
Step 1: Find a corner.(not a box or crate, two big walls intersecting)
Step 2: Stand by the wall a little back from the corner.
Step 3: Let your partner do the same with the same distance.
Step 4: Slash/Shoot.
Step 5: Let you and your partner run into that corner at the same time.
Step 6: keep holding W and continue running into the corner and jumping. (try to jump at the same time, for me its when we hit the corner and continue jumping fast as we can.)
Step 7: With this you'll usually get alot higher than Fly gltiches but it is only used to reach roofs/edges.