Defeating The Boss!
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It wasn't a fair fight at all. Although the Boss had the power to conjure deadly Phantasmal and Shadow Magic capable of damaging and piercing souls, with the combination of my Soul Gear, my Soul Shields made of Aether itself, and my potent blows, the beast was unable to harm me at the beginning.
I was also too big of a target, too many areas to hit, too little accumulated damage. My soul had become stronger, and when I converged its Demonic, Draconic, and Titan powers into one, it became several times mightier.
The combination of Divine Soul Pierce and Piercing Blow created an amazing synergy, these two Divine Abilities ended becoming the core of my damage. Combining their effects with my Divine and Demonic Weapons quickly overwhelmed the "small" dragon, which kept conjuring phantasmal flames, storms of them, attempting to engulf me with them.