The original premise behind the series (depending on series release, comic adaption, or animated special) was that essentially all the monsters lived in a giant mountain or were being kept prisoner there until Warlock (the series never makes it fully clear if he is the only one of his kind or if he is the most dangerous) used some kind of elixir of shrinking to escape...but during his escape all of the mountain shrank as well. Now this bothers me to the end firstly due to the Square/Cube Law being Hand Waved and secondly if the WHOLE mountain shrank doesn't that mean they all were still trapped??
The US short run comic and the UK long run comic started out about the same, the story line divided about issue 2 and in the US at least the comic book was killed by issue 4, the last of the mini-series run. The UK comic ran for at least 6 issues — I am surprised it didn't last longer as the figures ran from 1991 - 1998 and even had a revival in the UK in 2006.
Spain translated the books from UK and redistributed them in a 12-mini comic style format complete with puzzles, games, and word searches splattered inside each book. It was a poor attempt to gain popularity however as the mini-books sold for the same price as a normal translated book would have.