I taken tetrahedron which is pyramide with triangular sides. Then I connected 2 of them in one figure in meshmix. Printing in one set is a quite nice challenge. Need support below 20 degrees and a good brim, because the reversed pyramide touches the base only a few millimeters and it is hard to print in stabilizing. But put them standing it is a real challenge!You see on photo, how I printed. Set support for less than 20 degrees to keep the reversed pyramide stable