The clog is a large, hairy and cycloptic entity seemingly mutated from a variety a chemicals who appeared in The Super Mario Bros. Super Show!
In The Super Mario Bros. Super Show! live-action segment "The Marios Fight Back", the clog, originally just a normal clog stuck in a sink, is mutated to its monstrous form after apparently absorbing some Mario Brothers Clog Cleaner and Mario Brothers Plant Food. Dragging itself out of the drainpipe it is stuck in, the clog attacks the first person it sees, reporter David Horowitz.
Trying to bite David Horowitz's arm off, the clog is eventually left alone in Mario Brothers Plumbing when David Horowitz manages to pull his arm from the clog's mouth and flees the apartment.
Later, Mario and Luigi, returning to their apartment after getting some pizza, find the sink they were to unclog in complete working order and David Horowitz gone and assume that, after seeing that Mario Brothers Clog Cleaner worked perfectly, David Horowitz had left. Unbeknownst to Mario and Luigi, the clog, having pulled itself completely from the sink, is planning to attack them. Eventually hearing the clog's roars, Mario and Luigi, scared of the bizarre mutant quickly begin running from it, as the clog chases them through their apartment.