Fan Casting DC’s Tales From The Dark Multiverse Episode 2:

On his world, Batman used to be the hero of Gotham City who fought crime with his Robins. However, the city took its toll on the Bat and claimed the lives of all his sidekicks, forcing Bruce to seek more extreme ways to prevent the crimes he felt he wasn't fast enough to stop. Batman set his sights on his world's Flash, determining that he could use the Speed Force better than the speedster himself could. Batman took out all of the Flash's Rogues and confiscated their weapons to use against the Flash in a fight for his powers. After Bruce bested Barry, Batman drove the two of them into the Speed Force using his Batmobile merged with the Cosmic Treadmill - absorbing the Flash and his powers. When Batman returned from the Speed Force, he donned a new costume and became "Batman: The Red Death" and began murdering members of his own rogues gallery in Gotham, despite the consciousness of Barry constantly pleading to him to stop.