This is a simple dice with a skull-shaped void inside it. In order to see the skull you need to use a transparent print process. Theoretically SLA should work (but lacking an SLA printer I haven't tried). For FFF printing, Colorfabb HT will work if you can print it hot enough and have an enclosure and can turn off the fan and turn your settings down to print fairly slow. See the video for ideal print settings.
This must be printed without supports or it will ruin the void.
There's still some question about orientation. The skull can't print facing up, the eye holes need support, so should I print it on the bottom or the side? The bottom tends to be very clear, but if you haven't had a perfect purge that's a no-go. But on the side any bubbles in the print become very visible. There's no clear answer to this one, pun intended, but I think if you printed these I'd say skull down, and that's how I uploaded it.