Artistic: (
Style) Titles which are showily or pretentiously artistic.
Horror: (
Genre) Self-explanatory.
Tragedy: (
Genre) Animes of this type have tragic events as an important part of the story, and usually will show how the characters are dealing with the consequences of that tragedy (more or less successfully). This doesn't necessarily mean the story cannot have a happy ending as the tragedy might occur during the first episodes of even before story begins; as such this category information need not be a spoiler (unless the tragedy were to be a surprise for the audience in a mystery-style show).
