Unfortunately, it's important for freeform tags to be specific and clear in interpretation, as vague tags or tags based around vibes can lead to a less than enjoyable experience for participants and can be very hard to moderate. The tagset already has Friendship which should work to indicate that you would like a gen fanwork with friendship in it. I could also add the tag Horror if you would like, and you'd certainly be free to add a DNW about changing the canon setting too much to your sign up.

Would Inspired by Dungeons & Dragons fit your needs for the D&D tag?