Cave
From SMWiki
Common Elements
In SMW, cave levels featured a rocky foreground (GFX1A) and a background featuring stalagmites and stalactites (GFX0C) or Layer 3 graphics.
Cave levels often feature low ceilings and narrow paths to represent being in underground tunnels, as well as adding a unique challenge compared to outdoor levels. Enemies such as the lava dwelling Blargg, the Spike Top, and the Buzzy Beetle, are commonly used. Lava hazards also represent a unique challenge to players, offering instant death for mis-timed jumps in more places than just the bottom of the screen.
In Hacking
In hacks, cave levels usually implement dark colors or shades of black, browns and grays to give the feeling of being underground. Cave levels are generally harder than grasslands. Restricted movement due to low ceilings give players less leeway for their jumps, and since a cave may have many tunnels or pipes, puzzle elements such as finding a P-Switch to advance are commonly used.

