Purim
There is a tale in the Hasidic Chabad movement that supposedly Joseph Stalin died as a result of some metaphysical intervention of the seventh Chabad leader, Rabbi Menachem Mendel Schneerson, during the recitation of a discourse at a public Purim Farbrengen. Stalin was suddenly paralyzed on 1 March 1953, which corresponds to Purim 1953, and died 4 days later. Due to Stalin's death, nationwide pogroms against Jews throughout the Soviet Union were averted, as Stalin's infamous doctors' plot was halted.
Sergey Kirov
On 1 December 1934, Kirov was shot and killed by a gunman at his offices in the Smolny Institute. There is a widespread belief that Joseph Stalin and elements of the NKVD were behind Kirov's assassination, but evidence for this claim remains lacking. Kirov's death was later used as a pretext for Stalin's escalation of repression against dissident elements of the Party, and disarming of the Party (every Party member was issued a revolver up to that time, when Stalin had them all taken away), culminating in the Great Purge of the late 1930s in which many of the Old Bolsheviks were arrested, expelled from the party, and executed. Complicity in Kirov's assassination was a common charge to which the accused confessed in the show trials of the period.