Transformers, G. I. Joe and He-Man are all television shows designed mainly to advertise toys. Comics are no strangers to creating comic simply to sell merchandise. Marvel Super Heroes Secret Wars is an example of this as it is tied to the toy line of the same name.
The Beyonder was a cosmic entity that observed and was fascinated by the Marvel Comic superhumans. As such, he sent the X-Men (which consists of Professor X, Rogue, Storm, Colossus, Wolverine, Cyclops, Nightcrawler and Lockhead), Spider-Man, Magneto, Hulk, the second Spider-Woman, the Fantastic Four minus the Invisible Woman, the Avengers (Captain America, Hawkeye, Captain Marvel II, the Wasp, Iron Man II, Thor and She-Hulk), the Wrecking Crew, Doctor Doom, Absorbing Man, Kang the Conqueror, Doctor Octopus, the Enchantress, Volcana, Klaw, Ultron, the Lizard, Titania, Molecule Man and Galactus to the Battleworld, which is a planet he made. He put alien tech on the planet. Despite the fact the only explanation of the rules being "Slay your enemies and all that you desire shall be yours! Nothing you dream of is impossible for me to accomplish!", he leaves the various characters to their own devices. The heroes and villains had several fights. Doctor Doom got a chunk of the Beyonder's powers and killed all the heroes. However thanks to Klaw's manipulating him and being as dumb as a brick, Doom brought them back and the villains are defeated. Most of the character (with the exception of the Thing, who decides to stay and explore the galaxy) are sent home. The only really notable things that have any lasting effect is introducing some new minor characters, Colossus ending his relationship with Kitty Pryde and Spider-Man getting the black alien suit.