Donnie Yen is a kung fu creative consultant and provides facial and motion capture for Mo Yuan.
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Donnie Yen's confirmed role
S-GAME says Donnie Yen has been a creative consultant on Phantom Blade Zero since 2023, contributing to its kung fu style and action design. He also provided facial and motion capture for Mo Yuan, the leader of the Bastion of Mo.
What this means
The announcement connects Yen directly to the game's action design and one character performance. It does not say that he directed the whole game, wrote its story, or performed voice acting in any language.
About Mo Yuan
The official pre-order announcement names Mo Yuan and identifies him as the man shown holding an infant in the new trailer. PlayStation's current event announcement identifies him as Soul's father. Further character history has not been confirmed in the sources used here.
For the spoiler-light setting, see Story and Setting. For official combat information, see Combat.

Story & Setting
State of Play