History-sheeter is an Indian police term for a criminal with a long record of serious crimes. The term originates from history sheets (similar to US rap sheets) maintained by police stations across India.
A prosthetic patch was created to match the actor's skin tone and applied around his neck. The patch had tubes attached to it. When Munna cuts the patch on the actor's neck, the prosthetics designer, who was sitting outside of the frame, pumped blood through the tubes. This is the blood we see coming out of the actor's neck.
The montage sequence that shows that the homespun gun business is booming under Guddu and Bablu was shot over several days, across the whole shooting schedule of Season 1.
In this scene, RS Maurya has been summoned by his superior, who is an I.G., which is the short form for Inspector General of police. Currently in India, an Inspector General of Police is a two-star rank IPS officer and holds the second-highest rank in the state police hierarchy, just below the Director General of Police (DGP).
The footage of bodybuilders that Guddu watches was shot by the show's co-producer, Abbas Khan, for a personal project.