From Bulbapedia, the community-driven Pokémon encyclopedia.
Izabe Island (Japanese: イザベ島 Izabe Island) is a large anime-exclusive island located between Mossdeep and Sootopolis. It contains a wide variety of environments, from desert areas to snow-covered mountains. Its highest peak is known as the Square Top, a cube-shaped rock formation on a mountain. The group traveled across the island between the episodes A Cacturne for the Worse and Do I Hear a Ralts.
The island was the location of a number of important events such as May winning her fourth ribbon in her first contest against Harley, the evolution of Brock's Lombre, the capture of Ash's Snorunt and Max meeting a Ralts that he promised to start his journey with.
Pokémon seen on Izabe Island