" Cheng Jialin " might be referring to " Cheng Jushu " in " Celebrating Years." Cheng Jushu was a master of Northern Qi. In the play, he always wore a mask and did not show his face.
The Joker cutting his face off is a symbolic act of completely letting go of any pretense of normalcy and embracing his insanity to the fullest. It's a shock tactic to terrorize and confuse his enemies.
'A Face You Shouldn't Show' manga has gained popularity due to its compelling storyline that takes unexpected turns. The characters have depth, and the world-building is immersive. Also, the way it handles emotions and conflicts makes it stand out.
His face might get red because he is embarrassed. For example, if he makes a mistake in public or is caught in an awkward situation, blushing can be a natural reaction.
It could be that the story has been removed for legal or copyright reasons. Or perhaps it was only available for a limited time and that period has ended.