Welcome to the forums, Stopper!
Generally, films based on movie/game franchises are welcomed by the creators. There are a lot of brickfilmers out there who focus on IP films, IP meaning "intellectual property", referring to other franchises that are tied with LEGO. Think of Marvel/superhero brickfilms, or Harry Potter, or Star Wars. Parodies are quite popular both amongst brickfilmers and viewers, and won't get you in (legal) trouble.
Opinions on this are slightly divided in the community over here. Some people feel it's easy to do these sorts of films because you don't have to create original characters or storylines to make your film. Most people think it's fine, though.
Regarding legal troubles: try to stay away from copyrighted music from films or video games. Especially on YouTube, companies are actively on the lookout for this. The worst case scenario is that your video might get taken down. If you're planning to use sound effects or voice lines, you don't really have to worry. (Unless you're using extended and unedited audio clips of whole scenes.)