The posthumous trial of Pope Formosus (816-896 BCE) reads like bad fan fiction. According to Wikipedia,
Jean-Paul Laurens, Le Pape Formose et Étienne VII (“Pope Formosus and Stephen VII”), 1870 (note the latter is now called Pope Stephen VI)
Pope Stephen VI, the successor of Boniface, influenced by Lambert and Agiltrude, sat in judgment of Formosus in 897, in what was called the Cadaver Synod. The corpse was disinterred, clad in papal vestments, and seated on a throne to face all the charges from John VIII. The verdict was that the deceased had been unworthy of the pontificate. The damnatio memoriae, an old judicial practice from Ancient Rome, was applied to Formosus, all his measures and acts were annulled and the orders conferred by him were declared invalid. The papal vestments were torn from his body, the three fingers from his right hand that he had used in consecrations were cut off and the corpse was thrown into the Tiber (later to be retrieved by a monk).
Following the death of Stephen VI, Formosus’ body was reinterred in St Peter’s Basilica. Further trials of this nature against deceased persons were banned, but Pope Sergius III (904–911) reapproved the decisions against Formosus. Sergius demanded the re-ordination of the bishops consecrated by Formosus, who in turn had conferred orders on many other clerics, causing great confusion. Later the validity of Formosus’ work was re-reinstated. The decision of Sergius with respect to Formosus has subsequently been universally disregarded by the Church, since Formosus’ condemnation had little to do with piety and more to do with politics.
Bartolomeo Platina writes that Sergius had the much-abused corpse of Formosus exhumed once more, tried, found guilty again, and beheaded, thus in effect conducting a second Cadaver Synod, while Joseph Brusher says that “Sergius [III] indulged in no resurrection-man tactics himself” and Schaff, Milman, Gregorovius, von Mosheim, Miley, Mann, Darras, John the Deacon of Naples, Flodoard, and others make no mention of this story.