Complex sentence: A Fiji mermaid (also Feejee mermaid) was a common feature of sideshows which was presented as a mummified body of something, supposedly a creature that was half mammal and half fish (like a grotesque version of normal mermaid stories).
Split into simpler sentences: A Fiji mermaid (also Feejee mermaid) was a common feature of sideshows. It is presented as a mummified body of something, supposedly a creature that was half mammal and half fish (like a grotesque version of normal mermaid stories).