A Superellipse is a form between a square and a circle. This can be done in 3D too.

 A normal dices motion, with flat sides, is stopped on each side. While a super elliptic form let the dice not only role over the edges but also along the sides and so conserve momentum. 

This dice just role smoother and with a bit odd motion as it wobbles.

So rolling gets more exiting as it can tilt unexpectedly the last moment.

Printing:

The orientation is on its corner to allow most equal sides.

Supports are not needed but use a raft.

Don't use infill as there is no 3D symmetrical infill - better use multiple perimeters