Elliot is most well-known for his role in the 1888 New Year's Day attack against the McCoy family during which he and a group comprised of other Hatfield men ambushed their rivals' home on Blackberry Creek in Hardy, KY. During the attack, the Hatfields shot and killed Calvin and Alifair McCoy, two of the children of clan leader Randolph McCoy, in addition to severely beating their mother, Sarah, before then setting the home on fire. Accounts, based on Mounts's later confession, state that the attack turned violent after Johnse Hatfield prematurely fired a shot, thereby causing his men to follow suit and the McCoys to retaliate. Confused by the sudden chaos, Mounts claimed to have mistakenly shot and killed Alifair while one of his relatives fatally wounded Calvin.
Public opinion is said to have acknowledged this attack as the most atrocious occurrence of the feud, and it was not long before a bounty had been placed upon the heads of the men who carried out the attack. Consequently, it was only a few days later when bounty hunter Frank Phillips chased down Jim Vance and Cap Hatfield, the leaders of the attack, killing Vance in the ensuing fight. He then rounded up nine other Hatfield men who were connected to the attack, including Mounts. The men's case famously went all the way to the U.S. Supreme Court, who ruled their crime was serious enough to warrant a trial, which began in 1889 and ultimately found eight of the Hatfield men, who were represented by attorney Perry Cline, guilty and sentenced to spend the remainder of their lives in prison.
The ninth man, Mounts, unlike his accomplices, was not represented by Cline and instead plead guilty and admitted to the murder, presumably under the impression that it would lessen his sentence. Though accounts indicate he was viewed as merely a scapegoat, an assumption furthered by Mount's last words, which were, reportedly, The Hatfields made me do it, Mounts's confession ultimately resulted in him being sentenced to death by hanging. Numerous feud historians also cite evidence of his possible innocence, as indicated by testimony given by one of the McCoys during the trial who claimed it was Cap Hatfield, not Ellison Mounts, who was the killer, and that Mounts had confessed under the impression that his family would save him before he could be hanged.
Mounts was executed on February 18th, 1890, and, though public executions were against the law in Kentucky, the notoriety of the feud led to officials arranging the execution to take place at the base of a hill along Kentucky Avenue in Pikeville, KY, in an effort to provide a clear view for the thousands of spectators who gathered at the hilltop to witness Mounts's death. After his execution, Mounts was buried in an unmarked grave near the hillside where he was hanged.