Stagger, also shown in-fight as “BREAK,” is done by inflicting stagger damage from abilities or weapons and depleting the boss’s blue bar. When the bar completely your damage against the boss is greatly increased and they are no longer able to move for a 5s period. After they have begun to recover they will be immune to stagger damage for 5s, which includes the time it takes to recover their bar and ~2s after it is filled.

Assault cards’ primary function is to help the team break the bar, whether by buffing other team members or doing a lot of stagger damage by themselves.