Well, it's a devil riding on the back of a turtle. The turtle is covered in skulls. (part 2)

So I was doing some random reading today and came across a section all about the prevalence of turtles in mesoamerican funerary ceramics. I don't mean to say that this corresponds completely with the diabolito I bought, but I think there's some connection (see previous post about Ocumicho).

Apparently turtles were considered dimensional travelers who could move between earth, heaven, and the underworld. The shape of the turtle's shell was thought to resemble a cloud, and so it was associated with the heavens. Tombs in Oaxaca depict flying turtle-men, and likewise the sea turtle (which moves through the water as though flying) was capable of getting to the underworld via the sea. A post-conquest codex from Michoacán, the Lienzo de Jucutacato, depicts turtles helping people who emerge from a primordial cave to cross the ocean (and presumably settle Mexico). During periods of drought or cold turtles hibernate, as a corpse hibernates in a tomb awaiting another life. Likewise the tomb, as the home of the dead, was equivalent to a turtle's protective shell.