Sluggy the Unshaven
From the Super Mario Wiki
Sluggy the Unshaven is a massive Sluggy found in Super Mario World 2: Yoshi's Island. It is a mid-boss encountered in the fort of World 5. It is a see-through slug with a face, hair in various places and a visible, and hairy, heart. To defeat it, the Yellow Yoshi has to throw eggs at its heart, pushing through its gelatinous skin. It was originally a tiny, nontransparent Sluggy until Kamek used his magic on it.
In Sluggy's open-air room is an Egg-Plant. However, it is at the very edge of the room. Once Yoshi has collected enough eggs, the player must lob eggs at the slug's skin. Every time an egg hits the skin, it is pushed inward and the egg bounces off. Yoshi can then pick up the egg and lob it again. Once the skin is pushed back enough, Yoshi can shoot Sluggy's heart (which is the slug's weak point). After four hits, the heart shrinks until reduced to nothing, and Sluggy the Unshaven slides off the stage.
Sluggy is incapable of knocking Baby Mario off Yoshi's back, making this the only boss fight where stars cannot be lost. However, it continuously slides forward toward the edge of the room, making it necessary to defeat it before it pushes Yoshi off the stage into the pit.
Much like Prince Froggy and Naval Piranha, it is possible to see the boss before Kamek magically alters it. However, the player cannot destroy Sluggy before Kamek appears, like they can with Naval Piranha.
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