Almost forgot about this month's blogcarnival, hosted by the Dump Stat. It's all about mixing genres in role playing games. My point to make today is that fantasy is best fit for mixing with... anything. You might figure otherwise, but I've seen successful examples of: time travel with Dr. Who like time lords, gun slinging like in the wild west or more like in swashbuckler movies, Indiana Jones like treasure hunts with Arthurian knights on the side, exploding Death Stars...
Well, actually I must admit that mixing Sci Fi and Fantasy is a rather iffy subject. It doesn't always work, and if it does, it doesn't work for everyone. That also goes for the Sci Fi elements of time travel. I think that's because of two things.
Sci Fi Presumes Many Worlds
Science Fiction implies travel between many worlds, and once a Bird of Prey is hanging above your fantasy city, that also means there is a universe of Klingons out there, or a United Federation of Planets ready to phaser and torpedo your evil hordes out of existence. Any great conflict suddenly becomes very small and silly then. And playing a brooding fantasy hero who wants to save his small world is rather petty in this perspective. So, if you introduce Sci Fi into your fantasy campaign, make sure that the Sci Fi element is weaker than the fantasy element. If there is a bird of prey, make it hopelessly lost, with long range communicators failing, and weapons dependent oon some magick mineral. Or even dependent on magick users fixing the machinery. Make it obvious that even if there is a whole universe out there, no way that it's going to get in to your fantasy world. Except maybe the poor few fellows who were lost in time and space.
Sci Fi presumes Magick does not work
This one is not always true, but it does play a role I think. In Science Fiction science is paramount. Nothing defeats ultimate science, not even psionics. Psionics, like the “Force” can be very, very strong, but even then they stand no chance against a Death Star.
If you want to mix Science Fiction into your Fantasy world, you will have to resist this notion. Magick (and the Gods, Angels, Demons, and so on) will always be stronger than science. That is what makes fantasy fantasy. So again, if you introduce warp drives, gunpowder steampunk ships, force walls, robots... make them either useless compared to magick, or better still, treat them as magick.
This way a warp drive becomes a Magickal Ether Transportation Device, and a robot a Magickal Golem. Try it this way, and see how much you can pull off. Your players may even enjoy recognizing the stuff.
Have a good mixing and matching your genres into fantasy!