I've been floating around in the erotica world for a long time and there's not a lot that I can't wrap my head around when it comes to fantasy. Interspecies sex? No big deal. I once attended a great workshop given by the lovely P.C. Cast, on how to write interspecies sex that was um...illuminating (the trick is to start with the animals mating style - then let your imagination go buck wild). I was reading Vampire erotica light years before "Twilight" surfaced; before anyone even knew that there was such thing as vampire erotica.
Aliens with dual penises that can grow to accommodate any position and/or body type? Been there, done that. Shapeshifting big cats? Oh hell yeah! When I see a tiger, I see something entirely different; but I think that I've only encountered one Elf-themed book in all this time; and none of it was written from personal experience - as is apparently the case with this young lady. So take yourself over to The Frisky and check out Elf Sex in Iceland.
No - not that elf...
After doing some digging around, I even managed to find the blog of the young lady in the video, and for once - I'm kind of speechless. In any event, if you don't hear from me for a while - it's because I've gone to Iceland.
For research...yeah, that's it! Research!