The Mermaid is a minor character in DK64. She needs Tiny's help in getting her pearls back, which are hidden in a treasure chest that only Tiny can access. Tiny will receive a Golden Banana upon doing so. She later appears during the "auditions" for DK64.
The Mermaid reappears in a later Rare game, Banjo Tooie. There, four statues of her are scattered around the sunken city of Atlantis. Placing eggs in the lettered bases (labeled sigma (Σ), delta (Δ), pi (π) and omega (Ω) in a reference to the Greek-style architecture of the area) that they carry opens the access of the area's main temple.