Although King Crimson is Diavolo's main ability. He wields a sub-stand named Epitaph (the funny looking second face located on King Crimson), likely obtained through his alternate soul. With Epitaph, Diavolo can look 10 seconds into the future, and witness fate before it happens before him.
Epitaph's ability is not properly shown to the readers until Doppio's fight with the leader of the Hitman Squad of Passione, and as Doppio is only able to use Epitaph and two of King Crimson's arms, Doppio is unable to change any of the fates seen through Epitaph, but can prepare accordingly.
King Crimson vs. Metallica Part 3, Chapter 107.Diavolo is able to utilize Epitaph with much more success, as with all of King Crimson's abilities at his disposal, he can actively effect the fates projected to him by Epitaph.