From the Super Mario Wiki
Marching Milde is a giant Milde appearing in Super Mario World 2: Yoshi's Island. She is the mid-boss of World 4, encountered at the end of Marching Milde's Fort by the Yellow Yoshi.
Like a regular Milde, Marching Milde does not attack, instead simply walking left and right inside her large chamber, hurting the Yellow Yoshi if he touches her from any other side than from above. As is the case with Large Mildes, jumping on Marching Milde simply causes the Yoshi to bounce off without doing any damage. To defeat this boss, the player must instead Ground Pound on top of Marching Milde to make her split apart into two smaller versions of herself. Employing the same strategy against the smaller Marching Mildes makes them split into Large Mildes, which in turn split into regular Mildes upon being Ground Pounded. Once every Milde has been destroyed or eaten, the boss is defeated.
Names in other languages
||Clack Clack, the onomatopoeia used to describe the noise made by shoes.