This is a household shelf bracket, inspired by Viking knotwork design and gripping beasts. In particular, this guy came from something similar on the weather vane of a long ship. I have included an all-in-one STL file for printing, as well as the DWG cut files for the two parts which make it up, should you want to laser cut it from steel. He's been on GrabCAD for many years now, so I thought I would bring him over here.

Anycubic

i3 Mega S/Pro

No

Yes

.1 or .2mm

10%

I put it spine-down to the build plate, and use tree supports in Cura to support the whorls. In plastic, I would not make it much bigger than 80%, and be reasonable with your shelf load. A couple of pounds at most.