Any character, any universe, all smashed together on a developing, medieval world that's run by magic and dragons. Planet busters will be severely reduced in strength. Some magical shield BS I suppose can be thought up. The characters binding the entire universe together are from Godzilla lore. When a maturing SpaceGodzilla accidentally rips a hole in space time, many different beings from different existences are deposited on this conglomerate world. The characters will be ignorant of their or other characters existences. For instance, if you have Darth Vader as your character and someone else has Spider-Man, Spider-Man will not recognize Vader.