Can you take a video of him and upload it to youtube? Provide us a link to the video
Have you looked to see if Mang has any mites or lice?
Look in his ears to see if there is any pus or yellow waxy substance in them.
Does he have a discharge/mucous coming from his nostrils?
I'm sorry - I did not get an alert that you added photos to your post about his beak
https://www.backyardchickens.com/threads/please-help-mangs-beak.1283832/
His beak is fairly long and needs to be trimmed. Does he seem to eat o.k.? What do you feed him?
Here's a good article about how to trim the beak
https://www.backyardchickens.com/articles/beak-and-claw-trimming.74570/
You also had questions/replies on another thread, you may want to take a look at that too, not sure if you saw it.
https://www.backyardchickens.com/threads/mang-is-sick-help.1283308/