DC vs Marvel fights are fun to envision. As social beings we unconsciously draw thoughts, concepts and perspective from a collective bank. Little is truly irreverent and the only way to avoid being inspired is to never be born. Even a human child that never interacts with other humans will create what could be viewed as art/artifacts posthumously because music comes from sound which comes from existence. So comic writers, try as they might, can't NOT take fragments from the wholes of other writers to create and flesh out new creations. Gladiator of Shiar in Marvel was most definitely spawned from the legacy of DC's Superman: same power set, costume template, high code of honor. And what a great concept! Imagine the Man of Steel without a dependence on a yellow sun and his only vulnerability is his confidence in himself. Awesome!

In my DC vs Marvel, Nedula of Marvel would need to face a DC adversary of the spaceways (so ripped from the adventures of the New Gods or Teen Titans or Legion of Superheroes or Green Lantern or some massive universal crossover crisis). Definitely a villain, someone motivated by a grudge, vendetta or compensation of sorts. Maxima would be one consideration and I think with preparations and knowledge of Maxima's powerset, Nebula would utilize her weapons and soldiers thoroughly to erase the Queen of Almerac from existence. It would be a good fight too. But Maxima has been both hero and villain and has always been dedicated to the future of her throne, hence the hunt for the perfect groom and obsession with Superman. Nebula is unabashed evil. She is a member of the most merciless bounties in the universe. Another consideration is Blackfire, the space pirate and older sister to Starfire. Blackfire likewise has always been an extension of other more developed characters, in this case Starfire. Blackfire is driven and murderous. She employs obediant followers through fear and spreads her reign of terror for the joy of misery as much as for the spoils. Again, however, Blackfire has been retconned to be misunderstood and eventually she and Starfire bury the hatch against a common threat against Tamaran and take the throne jointly. Scratch. Another angle to branch ideas off from though would be the lineage issue. Both Nebula's father and grandfather refute any relation to the space pirate. In the DC universe, a similarly-driven to accumulate power and fear as acknowledgement of lineage baddie exists -- Grayven. The youngest son to Darkseid of Apokalips who used his life in obscurity conquering races and planets as he approached Apokalips in order to make his presence and ambition very apparent to his father. Nebula and Thanos bear a resemblance closer than Thanos to his brother or father just as Grayven resembles Darkseid more than his two confirmed sons Orion or Kalibak do. And Nebula has always been out to out-Thanos Thanos through murder and cruelty just as Grayven sought to overthrow Darkseid just as Darkseid had done to his father Yuga Khan.