yes, I made my engine, but it's a very small/simple one.
I think it complies with the 1 bit constraint because alpha blending are allowed.
Viewing post in Eat diamonds and switch the light jam comments
While it is allowed, the sprites themselves have shading; you can see it on the diamond: https://v6p9d9t4.ssl.hwcdn.net/html/8532817/atlas.png
It can be fixed easily, though; just dither it with Aseprite or any other pixel art tool.