Go back to the beginning, that was the plan. Stop Voldemort on the cusp of becoming a dark lord, stop him before he created his first horcrux and change history before it could be written. That was the plan, only Harry made a mistake.

Harry Potter was always called a "Freak" by the Dursleys, the wizarding world often reviled him, and the muggles ignored his abuse or added to it... After all of that abuse, is it any wonder that Harry is going to make the world regret it? W!Dark Animal H

Harry Potter catches Voldemort's AK to the noggin only to find out that his life is a video game and he forgot to save. So what does he do? Does he return on Hard mode and work for the challenge? Heck No! Harry uses every exploit, grind, or underhanded tactic he can get his hands on. His life may be a video game, but nobody plays Harry Potter; Harry's going to exploit the system.

What would happen if Harry Potter was the Master of Death from the time of his infancy? What if being "marked as his equal" meant that Harry was also on the path to immortality? Dark but not evil Harry. Powerful. Manipulative Dumbles, bashing.