This is a mechanic intended to give players a heroic ending for their characters who are about to die. I used this mechanic in my 5e games to great effect, so I decided to make a PF2 version of it.
Trigger you reach dying 4, or dying 5 if you have the Diehard feat, and have never used the Blaze of Glory action before.
As you feel your life begin to fade, you get one last surge of vigor to try and save your allies. You can stand up and immediately take two actions. Any attack rolls you make with these actions are treated as if you had rolled a natural 20. Any saving throws another creature would make due to these actions are treated as if they had rolled a natural 1. And any healing you cause with these actions is maximized.
After your actions are completed, you immediately die, and your spirit is at rest. Nothing can bring you back to life short of the power of a level 20 or higher artifact or a deity.