As the title says, Brakion takes half damage from damage dealt in a well of radiance. I cast the Well, so maybe it's just damage from its owner since it counts as Super damage. I don't know if this extends to all super and/or abilities. More information: Xbox Series S, 1809 power level, legend difficulty, solo. My izanagi honed edge x4 shot dealt 58,662 damage when standing outside my well. I then cast my well, stood in it and shot at the boss and it dealt 36,663 damage, which is exactly equal to 58,662*1.25*0.5 (weapon damage increased by 25% from well of radiance then halved). I linked an imgur gif of what happened.