I don't do mash-ups of my differing universes, despite the number of times that fans have remarked on how "cool" it would be to see Lord Loss team up with Mr Tiny, or Dervish take on the vampaneze, or Darren go out on a date with B Smith. My various series exist independently of one another, and for the most part that's the way I intend to keep it -- things can just get very messy otherwise, as we've seen over the years with the Marvel and DC universes -- sometimes (most times) it makes sense to quite while you're ahead.
(That said, there WILL be a small bit of a crossover between my next Darren Dash book and Lady Of The Shades, but it's only the teeniest of crossovers, a brief scene that will make readers of Lady smile, but that won't make any difference to anyone who hasn't read it. I don't mind the occasional little Easter Egg like that.)

However, I've no problem at all with fans mashing up my universes, whether it's in fan fiction or in drawings like this one sent to me by a young lady called Emma, which features Kernel Fleck from my Demonata series, and Darren Shan from Cirque Du Freak. I never read fan fic (it's just never appealed to me), but I love looking at fan art, and this one tickled my fancy big time. I hope it makes you guys chuckle as much as it made me giggle! :-)