There are different speculation as to who is the final boss, and few clues are given (1) He/She was already introduced years prior (2) He/She is stronger than the Heaven Smiting Devil Emperor.
let me just share my theory:
Currently Heaven Smiting Devil Emperor is the strongest the in the primal chaos and was the strongest devil back when the gods and devils were alive. So to produce a character stronger than her it should be another creation god/devil or someone who inherits their power. Mo E is undoubtedly the strongest creation god (apart from the evil god) and given his personality, he will refuse to die without leaving something in the world and how did he die from exhausting his life span if the gods have the Primordial Seal of Life and Death. My theory is that Mo E choose to die to leave his inheritance much like the Evil God and since He/She was already introduced years prior, maybe Xiao Lingxi for reasons that she can read the World-Defying Heaven Manual cause she has creation god/devil heritage. Why not Xia Qingyue? Because Xia Qingyue is the result of positive karma produced by the Mirror of Samsara to protect Yun Che. That is her mission and the reason why she and Yun Che are tied by fate. Another possible prospect is Ling Yun, Ling Yun is the perfect candidate, he is obviously not part of the harem, he is introduced years prior, and his existence and death doesnât affect the story, which made you question, why does he exist in the first place? The final battle would most likely replicate the battle between Mo E and Evil God.
Another theory is the corrupted daughter of Primordial Azure Dragon, weâve already forgotten her existence but she was already introduced years prior. The daughter of Primordial Azure Dragon is a true god sealed within the Heaven Punishing Ancestral Sword, much like Heaven Smiting Devil Emperor, she spend her life undoing the seal, and was broken due to the weakening of energy in primal chaos. And much like the Heaven Smiting Devil Emperor she will be full of resentment and rage. Controlling the Heaven Punishing Ancestral Sword, she will be the strongest in the current primal chaos, but this theory is far fetch
What do you guys think?