So, I was playing the freeware classic La-Mulana when I got to the area called the "Dimensional Corridor." I hadn't seen any spoilers about the actual area, but when I got to the boss chamber, I remember hearing that the boss was "Tiamat." Tiamat, the five-headed god of chromatic dragons from Dungeons and Dragons! This was going to the most awesome boss fight in...
Holy shit, Tiamat's a naga!
Fortunately, she can't eat the player character, as apparently eons-old guardian spirits don't have metabolisms.
In addition to being a naga, her powers of creation are second only to the Mother herself (the Mother is the goddess that created all of civilization in La-Mulana), and the dungeon she resides in has a few similarities to the Felarya setting. The Dimensional Corridor, as you might have guessed, is a corridor that is heavily implied to span multiple dimensions. Tiamat's boss theme is "Interstice of the Dimension" which basically means "the space between dimensions." Felarya can intersect with multiple dimensions, and it is heavily implied that Tiamat has some control over time and space.
If this doesn't smell like an excellent crossover fan work to you, I don't know what does.
I'll post the basic story outline I have in mind later.