The Mermaid Mansion is a gamepass in Adopt Me! which can be bought with 400.
The Mermaid Mansion comes in a bubble that surrounds the house and a couple of clams with pearls outside. Inside the house, it comes with a pool in the center and some sea-related furniture. It has a total of 4 spacious rooms. The owner can change the color of the shell by changing the color of the house.