Iron Cleft is a metal Cleft with impenetrable defense. They are seen in the Glitz Pit and the both of them are considered a mini-boss of the chapter. The two Iron Clefts are in a team called "The Armored Harriers". Before the fight they make fun of Mario due to false insults, calling him a "stinkwad" and saying it's impossible to be defeated. In reality, they can't be defeated unless they somehow slammed into each other. The first time Mario fights them he loses. After the Yoshi Egg he found at the Hot Dog stand hatches, he uses the Yoshi Kid's Gulp ability in the rematch against the two. Since this move involves an enemy being swallowed and spat toward another enemy, the Iron Cleft's brother pierce his defense, rendering it useless. Both of them are defeated and demoted to the Minor League. Later on, both of them are seen again and challenge Mario to a rematch. They are ultimately defeated the same way.
Interestingly, the The Armored Harriers would easily best Rawk Hawk due to their impossible defense and spikes on their heads. Rawk Hawk would be no match against either of them if they ever faced.
Another interesting to note is that they are one rank below "The Tiny Spinies" despite the two Spike Tops being weaker than the Iron Clefts. If they were a rank ahead of the them, they still can't go any further since The Poker Faces, the Bristles, has a trick of their own, not letting people attack them directly. Meaning they cannot defeat them.
All other major-leagers must have somehow been able to defeat them.