The Phantom Blade Zero final boss is Mó Yuan, played by Donnie Yen — who is also Soul's creative consultant on the game and provided the character's facial and motion capture. The unusual part is not who he is but how often you fight him: Soul duels Mó Yuan several times across the course of the game, and each of those encounters is designed to teach the player another layer of the core combat system.
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The same opponent, several times
Each Mó Yuan duel is a combat tutorial rather than a repeated test of one memorized pattern. Beating him repeatedly is the intended route to the ending, not a difficulty spike waiting at the credits.
That design also explains why boss fights are built in phases with a checkpoint at each one — you are expected to lose these encounters. How boss behavior changes between phases and across difficulties covers what makes a rematch different from the first attempt.
What the last fight is designed to do
Producer and director Liang Qiwei published a long piece on his own platform describing the final encounter. For the last one, he said that perhaps the only way to win is to forget everything.
He did not spell out what that means mechanically, so it should not be read as a confirmed rule. It could refer to accumulated stats and gear being nullified, to the boss having no fixed pattern that muscle memory can learn, or to the narrative framing of Soul's martial arts being dismantled one layer at a time. What is confirmed is the intent: the final fight is a deliberate contrast with everything before it.
What that means for how you should approach it
Because the fights before it are tutorials rather than endurance checks, the useful preparation is the whole combat system rather than one build:
Read the color flash
Blue parries, red dodges, uncolored blocks. Every boss, including this one, telegraphs with the same cues.
Keep Sha Chi full
Guarding is what drains it, and the final fight is long enough for a lazy defense to matter.
Use the super-armor trio
Power Surge, a Phantom Edge and an Execution are the only actions that cannot be interrupted, and they are what buys space when the pressure comes from more than one angle.
Do not rely on one memorized answer
The progression of these duels is deliberately built so that the layers you learned earlier stop being sufficient on their own.
The Phantom Blade Zero final boss, Mó Yuan
Mó Yuan is one of six revealed encounters, alongside the Seven Judgments, the Dancing Lion, a Drunken Sword boss, a Puppet Master and a hidden two-boss encounter shown at the end of S-GAME's showcase. Every revealed boss and how the fights are structured covers the rest of the roster and the phase structure they share.