Cobrat

Cobrats are large snakes (or most likely cobras) that jump out of the sand or vases in Super Mario Bros. 2. Most of them can spit out black projectiles similar to Snifits. They're in the desert levels and are easy to defeat if in a line; the player can throw one and cause a domino effect. They can be passed by easily and only pose a threat when in large numbers.

In the Super Mario Bros. 3 remake in Super Mario All-Stars and Super Mario Advance 4: Super Mario Bros. 3, one of the kings is changed into a Cobrat.

After a very long absence, they reappeared in Mario Pinball Land on the world Shifting Sands. They were inside the pyramid and were a common enemy. Oddly enough, they are green instead of red.

Cartoons
Cobrats appeared several times in The Super Mario Bros. Super Show!, where their size varied from miniscule to exceptionally large. The role of Cobrats in the show varied, as they would occasionally appear as enemy monsters and on other occasions, would be used as handheld weaponry, capable of firing small, exploding black orbs.

Comics
In the Nintendo Comics System story "Just Deserts", two Cobrats, capable of speaking, appear as inhabitants of Bowser's desert fortress; the story itself makes it ambiguous as to whether or not these two Cobrats are actually affiliated with Bowser or simply live in his pyramid fortress.

Trivia

 * The manual of Super Mario Bros. 2 says that Cobrats often appear in the dreams of Toad; this led some to believe that Toad had a fear of Cobrats which manifested itself as nightmares.
 * Cobrat is the portmanteau of 'cobra' and 'brat'.