I'm sure I just jumped on some bandwagon or other with this, but honestly
Jim Moriarty from Sherlock
and the latest* incarnation of the Master from Doctor Who
are totally soulbros.
They could have a spinoff together ("Gee, Master, what do you wanna do tonight?" "The same thing we do every night, Jim - try to take over the UNIVERSE!"
) aaand... uh, for all I know, they already have their own section at FanFiction.net and twelve fan groups on DeviantArt, I mean, their fandoms are huge and I'm a bit late to the party anyway, so, no matter what I come up with, someone must have thought of it already
*UPDATE. Uh, yeah, not anymore. My point still stands.