It feels like I remember someone finding a connection between X-Boy and Sintax before, but I may be imagining things.
I was surprised to see this version of Mulan, since I've seen a couple other boxes that seemed as much the original as any other. Now that I think about it though I never connected it with X-Boy. Since Hercules clearly uses the same engine, and that game is part of the ES-XXXX ID series(which also includes Sonic Jam 6 and Mario 1998 2 and Pocket Monsters), I wonder if they made all those games too.