Unless you want to get banned for edit-warring, stop it. The MonsterVerse category was removed because there aren't enough pages for there to be a separate category. 20 pages minimum are required for any category on this Wiki to qualify. Navboxes have nothing to do with why there isn't a category for it, NOR does the Godzilla Villains navbox somehow negate the Godzilla Villains category from existing.
There has never been a single rule on this wiki that has stated that franchise categories and navboxes can't coexist, so do not try and remove categories from pages just because a navbox is there.