A marker is found in Dressrosa and things slowly go to hell from there as Dressrosa's citizens are driven insane and the necromorphs eventually appear
Okay so this takes place after the timeskip but before luffy and crew arrive in Dressrosa
So the straw hats don't appear
Anyways the black marker is discovered in Dressrosa and sometime later its citizens are driven insane and commit homicidal and suicidal acts and eventually the necromorphs appear.
Now since the citizens of Dressrosa are normal humans even as necromorphs they will be no match for the Donquixote pirates.
That doesn't mean this story will be a curb stomp though.
The Donquixote pirates although powerful aren't immune to the markers effects and themselves will be driven insane by the marker.
For instance here is one idea I would like you to use, Pica is driven insane by the marker and in an insane rage he kills Dellinger before he kills himself.
An infector comes by and transforms Dellinger's corpse into a puker and Pica's corpse into an Enhanced pregnant.
Thus creating the first necromorphs out of the Donquixote pirates.
The donquixote pirates will then be faced with necromorph versions of their former comrades (who will be a lot more dangerous then necromorphs created out of regular humans and even as a necromorph Pica still has his Devil fruit power)
And later on other members of the Donquixote pirates may be driven insane causing them to turn on each other causing more deaths.
For instance a member consumed by Dementia might attack Doflamingo forcing Doflamingo to kill him.
How the story ends is up to you.
