Snailicorn

Snailicorns are large snails that have the characteristics of a unicorn, such as a large horn. They appear only in New Super Mario Bros. and are never seen outside of ice stages. They can be very dangerous, as a mere jump is not enough to defeat them, and fireballs are ineffective. However, as jumping on them sends them back a few feet, this tactic can be used to send them off of a cliff nearby. Also, a full-speed Koopa Mario, or stray shell will defeat them.

They can be annoying, as they are quite large in both height and girth, and are usually found near cliff edges, and under low ceilings, so there's not much leg room for the plumbers.

They will always charge in a straight line, but stop at edges like a red Koopa Troopa. Jumping on them at the last minute is a quick and easy strategy.

Trivia

 * Snailicorn's attack pattern is reminiscent of the Cleft species in the Paper Mario series.