Pure Vessel is a much harder version of the Hollow Knight, with all of their hazards and attacks dealing two masks of damage. They are also among one of the most difficult bosses in the game due to their rapid attack pace.
It is always recommended to jump prior to every one of Pure Vessel's attacks as a precautionary movement as this will help dodge most of them. The main two being the Lunge and Triple Slash attacks as these two occur most often and both can be avoided by using methods to try to leap or bounce over.
The Shining Daggers attack has the daggers set at random angles, and despite the beams of light indicating the direction of each dagger, it can be hard to position in a spot between two daggers. This leaves the best option to just use Shade Cloak to time and dash through the daggers. It is also recommended to stay a small distance away from Pure Vessel if dashing towards them as getting too close will cause the Knight to make contact with Pure Vessel and take damage. This attack also has a decently obvious cue as Pure Vessel will always attempt to teleport to the far side of the arena- or even off screen (Though take caution as in later stages of this fight the Void Tendrils attack has a near identical cue).
Diving Light Lances can require visual memorization of the distances of each lance in position from Pure Vessel as they will always shoot up in consistent rows in relation to where Pure Vessel landed.
The Focus attack is about the easiest to dodge as the build up is long and requires the player to simply start dashing away quickly. It is possible to heal after getting out of the major blast zone of the Focus as long as one of the other smaller explosions do not spawn on top of the Knight when healing.
Take advantage of Pure Vessel's large hit-box when trying to dodge the Void Tendrils attack as dashing close to them and then down-striking will catch the edge of Pure Vessel's hitbox and allow the player to bounce over. Otherwise simply dashing and then using Monarch Wings to cross the final distance over Pure Vessel is enough to avoid damage.