Sirenix Underwater is a series of Winx Club dolls by Jakks Pacific Winx Club released in 2013 (???). The dolls were exclusive to Toys R Us in the United States and Canada. Factory overstock dolls were common for many years on Chinese websites like Aliexpress and Taobao.
A playset was planned featuring Flora but was unfortunately cancelled prior to release. Jakks Pacific Winx Club unreleased.
This series is unusual for Jakks Pacific in that it features Musa as opposed to Aisha as the fourth character (as Flora was planned to be a character but was unfortunately never relased).