Marching Milde's Fort
From the Super Mario Wiki
When Yoshi enters the fort, he will find four doors to choose from. The first door contains plenty of Lava and Hot Lips. Yoshi must navigate an area filled to the brim with Lava but if Yoshi gets to the end of the area he gets a Key. The second area is a room filled with Bandits, Snifits, and Bullet Bills. If Yoshi can navigate this room with out getting Baby Mario stolen, he will receive a Key. The third area has lots of Thorns and Spike Bandits. It also has Ghost Arrow Lifts. Yoshi gets a key at the end of the area. The fourth area has every plant-based enemy in the game guarding the last key. If Yoshi can defeat them all, he well receive the last key.
Now it's time for Yoshi to use these keys in the center hub area where there is a locked door that Yoshi opens with the first key. The first room is filled with Marching. The second one is filled with other enemies in the floor and ceiling. The third one is filled with lava and some red coins along with a tilting platform as a bridge. The last room feature various of Mildes. It also has the entrance to Marching Milde's chamber where Yoshi must battle and defeat her.
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
This is the only fort level of the game where Yoshi doesn't start inside the fort, but rather outside.