Sluggy the Unshaven
From the Super Mario Wiki
“Aaaaah, Yoshi! To get this far you must be powerful, but remember: This slug has no weak points!!”
In Sluggy's open-air room is an Egg-Plant. However, it's 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, the skin will be pushed back and the egg will bounce 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 will pop out, 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, he continuously slides forward toward the edge of the room making it necessary to defeat him before he pushes Yoshi off the stage into the pit.
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