Sacred Haven of Debauchery

Actually, the laser turned out to be a minor issue; what’s much more unpleasant is that these red things change the trajectory of the projectiles in this environment, and the laser itself forces you to move in an undesirable direction.

Added after 29 minutes
Fortunately, this part includes a spell practice mode. After trying it several dozen times, I realized that this is the simplest pattern of all on this boss.