Underwater levels are rare, to much relief of the player, as these levels are generally regarded as slow, boring, or difficult. On the Overworld, underwater levels are indicated either by a regular level tile within a large body of water like a lake or ocean, or by a small pool of water surrounding the level tile.
Underwater levels are either spacious with plenty of room for Mario to swim, along with other enemies such as the Blurp and the Rip Van Fish, or cavernous with tight restricting tunnels. These will often implement floors and ceilings to prevent Mario from swimming past the level.
Hackers strive to avoid the negative stereotype associated with underwater levels, through numerous above-water sublevels, puzzles only possible with the free movement water allows, and fast-paced sections.
Underwater themed levels in SMW
|Level Themes found in Super Mario World|
|Bonus | Bridge | Castle | Cave | Grassland | Forest | Fortress | Ghost House | Mushroom (Theme) | Sky | Underwater|