This is a custom die created using the Customizable Giant D20. If you want to make your own, or see what other people have made, check out the links below!
Customizable Giant D20: https://www.printables.com/model/904821-customizable-giant-d20
Other Designs: https://www.printables.com/@CarlThePumpkinMan/collections/1495596
The author remixed this model.
I used the instructions to imprint a Boros symbol on the D20