Does anyone have any good 8-bit underground backgrounds?

[EclipseMain]

Weird question here, idk whether I should've posted this in general or the custom graphics section of this forum.

I'm making an 8-bit SMBX game. I built upon the CaptainObvious 8 bit graphics pack by recoloring stuff and converting some 16 bit sprites to 8-bit.

But I can't find any good underground backgrounds that'd go good in, well, any 8-bit scene. Right now I'm using this placeholder smb3 background but it's just dots, nothing special.



Does anyone know of any 8-bit underground graphics I could use? The original SMB1 uses a plain black background but it's boring as heck.