Except for Jesse Lynch, who seems to have survived hanging, most folks who get near Mr. Black end up dead. True, he's the undertaker in Tarnation, and everyone dies eventually. But the residents of a cursed town met their fate unnaturally soon, even by local standards. Some say Black can't be killed because he's already dead. I know only one thing for sure: every man who went after him was never heard from again.
Mr. Black was the undertaker in the town of Tarnation, before all of the residents mysteriously died. He runs a gang in the (now) ghost town of Tarnation. Although his first name is not known, Sheriff Bartlett's Journal indicates that it starts with "N".
Black had a bounty of $300, and is listed as "Dead as possible" in his journal's page in Sheriff's journal.
Red entered Tarnation cemetery after killing Jesse Lynch, Black's right-hand man. Black sent his men to kill Red, however they all were killed by him.
After a long shootout, Black himself was killed by Red Harlow. Ironically, he fell into his own coffin as he died. Red slammed the lid shut and hauled it back to Brimstone for his reward.
Mr. Black becomes available as a playable character in Showdown Mode by completing the mission "The Cemetery" with an excellent rating or by purchasing the Embalming Tools from the shop at the start of the mission "Sunset Canyon". His special ability is a machine gun mounted within a coffin that he carries. Due to the weight of this setup, he moves very slowly.
Sheriff Bartlett's Journal
Mr. Black is listed in Sheriff Bartlett's Journal on pages 160 - 161 under the Wanted - Dead or Alive section. The pages are unlocked by unlocking his Showdown Mode character via either of the methods noted above.
Verne Wiggins mentions meeting Mr. Black when Verne's sister died in Tarnation.
The undertaker's store in Brimstone is closed with a sign that reads "closed due to death in family". This might have something to do with Mr. Black.
He appears to have a degree of "super-human" strength for he can take his coffin (with the Gatling gun still encased inside) and swing it at the player.
He is mentioned in Red Dead Redemption. When sitting around a camp sometimes someone will mention an "undertaker near here" that carries around a coffin with a machine gun inside it.
Mr. Black's weaponry is a reference to the 1966 spaghetti western Django in which the protagonist has a Gatling gun concealed in a coffin.