At the final battle between Giorno and Diavolo in episode 38. Diavolo got punched many times, and almost drowned in the river.
He survived that and able to catch the edge of the sewer stairs, which kept his body floating. Poorly, he met a burglar/homeless man that stabbed him, and then he lost consciousness. Just after that, he looks like he's in a hospital bed, and a female doctor suddenly performs an autopsy on his body while Diavolo's alive. In the middle of the autopsy he suddenly teleports to a downtown area where he gets hit by a car, and last, he met with a child and for no reason Diavolo got scared.
What happens to Diavolo in episode 38 exactly? According to Jojo's Wiki, such stated
Gold Experience Requiem is a close-range Requiem Stand that boasts an incredible increase in both speed and power compared to its previous form. It also wields the arcane power of reverting anything to "zero", effectively undoing their actions; a power that trumps even the time erasure/nullification of King Crimson.