In Barbie Mermaid Adventure, Barbie assumes the role of a specimen of that mythical fish-human hybrid, the mermaid, and plans a party with all of her undersea friends. Unfortunately, a magical light shell in the main palace broke. In order to fix it, Barbie needs to enlist the help of 3 rainbow dolphins.
Each rainbow dolphin is hiding in its own area, either in Sunken Ship Cove, Kelp Forest, or the Coral Reef. In order to find the dolphin, Barbie must find 3 musicians in the area so that she can ask them to play at her party; and she must solve 2 minigames in each area. Each area has a maze game where Barbie must collect an accessory that she will be able to wear at the party (necklace, crown, and earrings). Other minigames include a Breakout clone, a matching game, and a puzzle game in which Barbie must rock all of the baby cuddlefish to sleep while not waking others who are already sleeping.
Additionally, the game includes activities to decorate the collected accessories as well as the party stage. Finally, the player gets to watch the aquatic celebration.