All of the original work I produce is (and will always be) available for free—shared under a Creative Commons or equivalent licence. You’re also free to share, remix, and build upon it as you wish, as long as you follow some simple rules.
No commercial use. You’re not allowed to sell the content directly and you’re not allowed to make a profit out of content you remix or build upon. If you’re an individual (i.e.: not a company), then it’s fine to make a profit out of content you remix or build upon.
Give attribution. Especially if you’re sharing the content directly, give credits where they’re due.
Don’t be offensive. Don’t use any content I produce in contexts that are racist, sexist, homophobic, transphobic, ableist, or that would otherwise be in violation of my code of conduct.
Note that this cannot be extended to fanart (or anything involving real people), as I don’t have the rights to extend to you in the first place. You can still remix or build upon it as you wish as far as I’m concerned, but you’re pretty much on your own there.