Thoughts about the Mask Man

The masked man is too well acquainted with dealings in the palace to be distant from the throne (so, he can't be the butler, or Gao Ming or anybody without a high status), we just need to rule out the "suspects" through their interactions with ZH.
I think he isn't minister Zhao Bingwen, bc. he didn't treat well ZH when he came to his home. I exclude prince Yongrong as well for similar reasons and among all the ministers we've seen till now, the only one that could eventually be him is the old and fearful minister Lu: he is a perfect "outsider" but with a status and close enough to powerful people.
The masked man could be a "third killer" bc. he was on the spot (rescuing young ZH), but the third killer must be someone working for Dongxia, that's why I don't think he is the third killer, in dialogues he doesn't appear to side with Dongxia

 itsvasuda:

This might be out there but I feel like it is the emperor. I know that seems a stretch and how emperors don't really move about like that, however he is seen taking a great deal of interest in woodcarving. I feel like the emperor is using zang hai to clean up court and find the gui seal. Or it could be his enunch (not cao). the masked man is also very well informed and able to show up at Zang Hai's house.

Can't be the emperor because he personally rushed to save Zang Hai.  No emperor will do that.  They tend to use their bodyguards.

He claimed to be Kua Duo's best mate who was late on rescuing his family.  Someone from Dongxia?

Ok Queen Dongxia is ruled out based on the 30th episode 😅

 Thuyanh:

What if the masked man is Queen of DongXia?

That's what I thought too

If it was the emperor. That would be a twist.