My daughters wanted some unicorn horns, so I modeled these up and printed them. They look really good in a translucent material, then you can stick in a lightstick and they glow in the dark!
I printed the Horn as a spiral vase with a wall thickness of 0.8mm and no bottom (in slicer). Put a fan on it, it'll help with quality towards the end.
For the clip, print however you want. I used 0.1984mm @ 15% infill.
I used some off-the shelf elastic from Ben Franklin, but the slots and clips are designed to accommodate a 1mm x 9.5mm band, so whatever works. Just use em like regular straps, and you can change the fit, or just sew em, and throw those little bits away.
It helps to squeeze the base of the horn a little bit to pop the clip in, but it holds well.