I just binged the series so it's fresh in my memory!
The person that took over Butler in school and told MC to use him, is definitely not Mu Han. They're the mystery person in ch 72 using the fox avatar.
The mystery somewhat annoys me because all the players have yet to be confirmed. We know Ex-fiance and commoner girl are players.
I have suspicions the culprit that stabbed irl Mu Han is FL's father.
-We know that he wasn't too keen with Mu Han already
-FL's in-game father is a coward, used her as a scapegoat (knows she has amnesia, but still told Butler she knows where the treasure is and puts her in danger by getting kidnapped), if the game somewhat reflects reality, then it's possible
But if the assailant is only narrowed to the Dream development team, then I think it's the player behind ex-fiance. Just because the in-game version has a plushie of Dream; the assailant wanted to steal Dream.
I just realised your comment wasn't recent, and was a month ago, before ch 72 was out :3
Damn!
Mu han is suspicious when the fl started talking about how she saw Mu han get hurt, he seem like he wanted to do something to her, he started searching for the gun, luckily she had it. But like why would he give her a killing intent, that scene made me realise that he might not be Mu han at all or maybe the butler is the real one? Then she said she doesn't remember the face of the attacker, then he relaxed. All I can I say, the guy Mu han might have changed her memories or might be acting as if he is Mu han.