As a fan of the comic strip, Warren Beatty wanted to put in as many characters from the comics into the film as he could. This was a measure used by Beatty in case the film didn't have a sequel.
Though Al Pacino had his own slicked-down hairstyle, the make-up artists had to add a fake chin, nose, upper lip, a mole on his cheek, and plugs behind his ears to make them stick out in order to turn Pacino into Big Boy Caprice.
Danny Elfman was hired to compose the film score because Warren Beatty was impressed with his work on Batman (1989). Of working with Beatty, Elfman has said "Warren was insane".
Big Boy Caprice: You know, Dick - You mind if I call you "Dick"? My associates here would very much like to see you have a little accident. But I tell 'em, "No. I'll take care of Tracy myself," I tell 'em. You know why? I want you on my side!
Numbers and Mumbles are the only prominent characters to survive. A few others that Tracy had arrested in the montage are assumed to have survived such as Ribs Mocha and Tex Garcia. 88 Keys also lives, but is arrested (if you consider him a villain, and not a victim of circumstance.)