What the subject says
My guess is it is shadows rendering wrong. Mind specifying the device, or at least the OS?
btw, you should post the OS of your mobile in the future – only reason I know that’s an android is because of the buttons at the bottom. And yeah, lighting has never worked optimally on androids. It used to be that the characters were really, really shiny and reflective for some reason.
[quote] What the subject says
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We do not support playing through BlueStacks. The latest version of the app might fix this bug anyway.
I have a wild guess that you need a graphics card that supports ETC.
Wops, forgot to say i use bluestacks to test android, because roblox don’t support my android phone that well ( i had to cheat install it on my phone) also, latest bluestacks works perfect beside the black parts. Also max my card is up to date, and was bought last christmas.
BlueStack’s implementation of OpenGL may not properly support the functions or extensions we’re using. Are you using the latest version of the app (176)?
Mainstream desktop graphics cards do not offer support for ETC.
I had the same issue on my Android Galaxy S3. I’m not sure if it is still happening though, and I’m getting a new Android phone in a month so I don’t really mind.
I have an SIII right now. 
So if anyone needs tests on the SIII or the Note I (My father installed Roblox on there), let me know. 