I have probably already posted at least two questions similar to this one. And now there are new categories. Faust-dammit.
Now, I get what most of those categories mean, but can somepony please explain me the definition of drama and mystery (apart from investigation and such)?

4838262 Mystery qualifies as one overarching question that is the main driving force of the narrative.

4838265 Thx. And about drama, if you know?

4838276 Here's what I could find.

4838262
While Smaug already provided a link to a very overarching definition of 'Drama,' I'll try to explain using it on this site. My guess is, considering Drama is such an all-encompassing word, that a lot of fics already published may qualify as 'Drama.' Basically, as taken from the Wikipedia entry, if the fic involves "focusing on in-depth development of realistic characters who must deal with realistic emotional struggles," then I'd say it qualifies as a 'Drama.' This could include Slice-of-Life fics, Adventures, Romances, Tragedies, Sad fics, a very, very wide range of fics which could probably include almost any tag offered (which, again, is why I said before that it's such an all-encompassing genre, something which the Wikipedia definition notes as well). I made the choice myself to add the 'Drama' tag to my Adventure and Crossover fic, "Batmare Begins," since I felt there's enough instances of characters developing and emotionally struggling that it did indeed qualify as one. So in sum, I think if there's the slightest bit of realistic character development in a fic you publish which either seems true enough to the show, the characters, or just serious enough in general, then it'll probably qualify as a 'Drama' in some regard, unless of course the character development is completely ludicrous since the fic is an off-the-wall Comedy. Hope this answer helps.