Oh! Well, there are a few, I'd like a crossover with Doctor Who:
- Avatar the Last Airbender/Legends of Korra
- Deep Space Nine (Possibly because I really am into an idea of a regenerating/reincarnating immortal support group.)
- Stargate
- Farscape, maybe John meets the Doctor first as Nine around season 3? And then again as Twelve or Thirteen post-series with Aeryn and John
- Legends of Tomorrow (for the shenanigans)
- Buffy
- Firefly
- Other Star Trek: Voyager and Discovery
I already wrote a Person of Interest and Criminal Minds one, sort of.
In-Universe crossover: Thirteen meeting Bernice Summerfield, Class, and the kids from Sarah Jane Adventures