Sewer
From the Super Mario Wiki
A sewer is both an element of Earth amd Mushroom Planet. It is common knowlege that they are used to carry sewage from toilets, sinks, bathtubs, showers and other water using applications. Sewers have appeared in the Super Mario Bros. Movie and may have appeared in the early Mario game, Mario Bros. In the Arcade/Game & Watch game Mario Bros., Mario and Luigi are assigned to clean out the "monsters" inhabiting them.
[edit] Notable "Sewer Creatures"
In the real world it has been fabled that aligators or crocodiles live in sewers but in the Mushroom Kingdom it is very common to have cretures living in sewers such as:
Shellcreeper: A turtle-like enemy that simply walks around. They take one hit to flip.
Sidestepper: Crab-like enemies that are slightly faster than Shellcreepers. They take two hits to flip.
Fighter Fly: Fly-like enemies that hop around on platforms. They can only be hit from below when they're touching the floor.
Slipice: A block of ice that slides around, until it stops on a random platform and freezes it.
[edit] Sewage
Sewage is anything that is unsanitary such as wastes or clogs.
