From the introduction:
Within these pages is the first dive into the world of the Retroverse. It is intended to be bombastic, humorous, and more than a little silly. The Retroverse is a universe inspired greatly by music, games, books, movies, and fashion of the 70’s 80's, 90's and early 2000's. It resides in a place of half faded memories, barely remembered songs, lost childhood friends, outdated styles, and time corroded files. This world does not follow the traditional rules for fantasy settings but is mired in them all the same. The Rule of Cool is written into the spirit of this game and is the only one that should be adhered to strictly. As with all things, your Game Master has the final say in how their world operates.
The Retroverse was built around 5E. There should be little problem bringing existing 5E content into this world or taking Retroverse content into another 5E setting.