Paper cave: I think ceilings are underused for interior decorations. Would love to try some more colorful paper or plastic cones on our ceiling. At least in a small section. It would also be a great way to add too a "man cave".
Paint mini canvases, put together in square, use squeeze bottle to swirl white paint over all of them. (middle three diagonal = same color; two top diagonal=same color; two bottom diagonal=same color; top corner on color, bottom corner one color)