Cannon Fodder
William's expert-like movements and fluid decision making were even more advanced than how he reacted in battle, the vials catching everything without letting a single drop go to waste. When one hundred vials of Solar Nectar were stored safely in his Space Ring, William returned his attention to the Boss.
Despite its best efforts to recover, the Sun Stone Golem was powerless to stop William. One by one, the Comet Pellet Spell destroyed its remaining three joints while William collected the Solar Nectar.
When the Sun Stone Golem used its vitality as a last resort, William simply allowed Atticus to phase through the Boss' forcefield and swallow it whole like it had last time. A few empowered Spatial Slashes later and the Boss was dead.