When you initiate a dodge roll, your character gains complete invulnerability for a window of frames calculated from the moment of execution. Under Medium weight, frames 4 through 16 pass harmlessly through damage collision boxes, even if the weapon geometry visibly intersects your body.
A successful parry requires your shield's active collision frames (typically frames 4–10) to clash with the boss's swing during its damaging active frames. Triggering too early causes partial block chip damage; triggering too late results in a punishing direct counter-hit.
Every offensive or defensive maneuver depletes stamina. Entering negative stamina triggers heavy exhaustion recovery penalty, locking you out of dodge rolls. Resting at the bonfire cleanses posture, refills Estus, and resets the boss's stance.