30 Stuns with the M2 Falchion
The Order: 1886 DISCOMBOBULATED Trophy Guide
This can be done at any point in the game where you have access to the M2 Falchion weapon. Early on in the game (Chapter 1 / Scene: The Atrium) you will fight some enemies with this weapon. Although you will have more chances to use this weapon later on in the game, you can get this right here if you want.
The Stun (R1) will recharge and you have infinite shots with it. Simply pick some enemies and continuously stun them. You can reload the checkpoint or die and your progress will be saved.