From the Super Mario Wiki
Ameboid is an enemy that can be found at the gate from Smithy's Factory in Super Mario RPG: Legend of the Seven Stars. It doesn't have high HP, but if Mario and company fail to defeat it in a single attack, Ameboid will split into five individuals. They will have the same stats as the original. Outside of battle, they are merely small blue spots who become bigger and reveal themselves to be Ameboids when they are approached. Their relation to Smithy is unknown and may just be natives of his dimension. They are strong against jump attacks and weak against fire.
Chester's body appears to be a tan-coloured Ameboid, contained within his treasure chest-like exterior.
Ameboids are named after Amoeboids, which are amorphous unicellular organisms. The enemy's appearance (like a gelatinous Goomba, and their initial form as a tiny blue spot) and behavior (being able to split into multiple individuals) also reference actual Amoeboids.
Ameboid walking, view from behind.
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