Ultron(MCU) has taken control over 10 Sentinels from the Days of Future Past timeline who have adapted to every power thrown at them from their last Movie. Vision w/Mind Stone is also taken over by Ultron and his IronMan Drone Army is replaced by Rev-9 Terminators. He leads those forces to Sakovia and starts his plan from his Age of Ultron movie.
To combat this new threat the Avengers(as of the AoU movie) get an unexpected Ally in the X-Men from the DoFp movie and all the mutants shown in that film as well as the Fantastic 4 from both new and old movies.
Can the combined forces of heroes beat or stop the Robot Master and his new crew from accomplishing their goal?