Complex sentence: The mermaid finds Allen's wallet that he dropped in the water and goes to a sunken boat where she finds a map and looks in Allenstein wallet to find where he is from she then decides to find him in New York.
Split into simpler sentences: The mermaid finds Allen's wallet in the water and goes to a sunken boat where she finds a map. Using Allen's wallet to find where he is from she then decides to find him in New York.