Thanos has used the Infinity Gauntlet to create a trans-universal interface between the Marvel and DC universes. Finding out about the power and ambitions of Darkseid, they form an alliance. In possession of the DC Spear of Destiny, Darkseid's minions have created a clone, which is tuned to the vibratory wavelengths of the Marvel universe, which will allow Thanos to control Marvel heroes within the Spear's vicinity, as the DC Spear does with heroes in the DC vibratory plane, thus making both impervious to attack from their universe's heroes.
Martian Manhunter, having learned of these circumstances, calls upon Access, the only other known person with the ability to move himself and others between the DC and Marvel universes. The Manhunter contacts Reed Richards, and the two conceive a plan to exchange a small task force from each universe to retrieve the Spears from the universes where their different molecular vibrations will nullify its effects, and thus stop the otherwise unstoppable advances of Darkseid and Thanos in their respective universes. The Manhunter from Mars and Mr Fantastic will provide long-distance guidance to the teams who are not familiar with the different universes.
And if you believe all that, then you have an active imagination! Crisis in Multiple UniversesTask Force 52
Strategic Lead - Martian Manhunter
Squad Leader - Cyclops
Tech / Science - Iron Man
Stealth / Recon - Invisible Woman
Energy / Power - Captain Marvel
Universal conduit - AccessTask Force 616
Strategic Leader - Reed Richards
Squad Leader - Adam Strange
Tech / Science - Cyborg
Stealth / Recon - Miss Martian