The fate thing in part 5 gets a little more complicated because of the way King Crimson + Epitaph works. So Fate is a thing that is real and it applies to everyone, everything that is bound to happen will happen, so on and so forth. Epitaph has the hability to look 5 seconds into the future, so he can see what is 100% going to happen next. This is where KC comes in.
When he activates KC, Diavolo is no longer bound by Fate and can do whatever he wishes while everyone else is still bound to their fates. This is the moment he uses to move around and turn dudes into donuts.
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