Mobile

[Drag00n]

If you buy it on steam would you be able to play it on your mobile too?

[Leonard]

No, but the Humble Store gives you an Adroid version with the PC version.
https://www.humblebundle.com/store/super-hexagon?hmb_source=search_bar

You get a steam key, you can play it without steam, you can play it in your browser or you can download it on your Android phone. That game is more an exception so don't expect other games to give you an Android version there too.