Scenario: Batman and Superman are both doing a mission together when suddenly they disappear and end up on a planet.
Goku and Vegeta are fighting a small foe when they got teleported to the planet.
They later both realize that, they were taken to another universe.
The king there knew all four heroes and wanted them to battle it out at his tournament. They all accept the challenge.
Batman arrives there with his Insider Suit and his Batwing. The insider suit is new and improved, it doesn't need a recharge time because he made it to have unlimited power from an unlimited power source. So basically he can use any of the suits powers at the same time. It's made out of a strong material that Batman created, so its durable. His batwing is loaded with nuclear tipped missiles. The missiles are special ones, once they hit the person, it creates a force field around them so all the power it causes could just damage them. The missiles are also using a new type of propulsion that speed them up to high speeds. Batman can shoot the missiles at anytime.
Superman arrives there, he's at his prime at this time.
Goku arrives there being able to reach super saiyan god.
Vegeta arrives there being able to reach super saying 4.
Superman vs Goku
Batman vs Vegeta