Without any boring builtins, I've managed to write a FizzBuzz program which is 22 bytes long, beating the 05AB1E solution by quite a bit. If you want to check it out, you can find it at
github.com/maxbergmark/mathgolf , I'd love some feedback and some suggestions for future additions, since there are still 77 unused command bytes, and some operators that haven't been implemented for all data types.