
AU info, short version:
Dio is not Chaotic Evil. He tilts more towards Chaotic Neutral and occasionally Chaotic Good. Every single canon EVENT happens, though the WAY it happens may differ, such as dialogue; none of it is he a willing participant in, fate simply has its own ideas about who and what Dio Brando is meant to be and arranges things accordingly. If it CAN go wrong, specifically by way of making him seem evil and a right proper villain, it WILL go wrong. If it can be misinterpreted, it will be. He would much rather retire somewhere to live a life of quiet luxury, but events inevitably conspire towards things more grandiose. And more evil.
Dio has developed a very special hatred for fate and the way it's been destroying everything he touches for a century now, and has set out to kill God in revenge. No god means no fate, right?
There may be flaws in his plan.
The World!!11 has been altered a bit by the changes of fate and destiny. It is fully independent if it chooses to (it generally doesn't); its effective combat range is still 10 meters, though it can go MUCH further from Dio it is largely incapable of fighting and will choose to discorporate or retreat over combat when at these greater distances. It often reflects Dio's mood and temperament though lacks Dio's self control at actually SHOWING those emotions. It is perfectly capable of verbal communication but doesn't feel the vast majority of beings are worthy. When it chooses to follow its own opinions, The World's Joestar influence is pretty apparent; it prefers fighting for justice, loyalty and friendships, and scorns petty or pointlessly cruel behavior. It is however, utterly obedient to Dio and will follow any directives given without hesitation.
Dio likes to call it James in private.
For game purposes, beings capable of seeing spirits, ghosts, demons and the like are perfectly capable of seeing and interacting with The World.
... WHY all this nonsense?
1. I think it'll be fun
2. it'll make him easier to play in games
3. ???
4. Profit