From the Super Mario Wiki
Waki-Waki is a large tropical and volcanic island located in Lava Land; as well as having a large amount of Mushroom natives on it (the Aloha People), Waki-Waki also has various types of butterflies and an Ostro living on it.
In The Super Mario Bros. Super Show! episode "Too Hot to Handle", Mario, Luigi, Toad and Princess Toadstool traveled to Waki-Waki in search of its Fire God, who had promised to help them defeat King Koopa and free the Mushroom Kingdom. After a lot of trouble, Mario, Luigi, Toad and Princess Toadstool managed to save Waki-Waki from being destroyed by Fryguy and King Koopa, who had disguised himself as the Fire God, and their Lava Machine.