Universe 4 is one of five universes in the Epic Multiverse. It is known as the Future Epic Universe, and it can be reached by time traveling into the future as well as universe crossing.
There are many differences between the future and present Epic Universes. Since it is the future, technology is better there, and there are people like Builder Awesome Face who can create beings much stronger than themselves. Awesome Face is a cyborg there, though he can still turn into his giga form, and Future Soul Weegee is the same oddly enough.
When they were taken to the future by lazor face, X-Demon and Y-Demon were also taken through (the ones created by Z-Demon, and became transformed and much more powerful.