This 4-sided (tetrahedron) pyramid with a captive ball makes a great fidget toy. Rattle it, twirl it, or just print it and enjoy it. It is also a good test of your 3D printer capabilities.

This pyramid is 40 mm tall. Scale it to whatever size you would like.

It will need some form of support to keep the ball from detaching from the build plate during the print. I printed successfully using a standard support structure attached only to the build plate.

Larger prints may require additional support structures (not only to the build plate).

I designed this using FreeCAD part design workbench.

The base is sketched in the XY plane a triangle centered at the origin. A second smaller triangle, with the same orientation, is sketched onto a datum plane at a calculated distance above the XY plane. An additive loft with these two sketches forms the solid pyramid. A spherical groove, centered at the calculated centroid of the pyramid, hollows out the pyramid. Finally, a ball is added in the center of the pyramid. It is not centered on the centroid, but instead lays flat on the XY plane.

Yes, the pyramid has a slightly flat tip. I have not figured out how to make a pointed pyramid in FreeCAD part design workbench yet. Sorry for the inconvenience.