Sonic: Dark Abyss

Carnage, a guardian who was once banished, was accidentally released thanks to a scientist named Eggman. At first, Eggman wanted Carnage to defeat Sonic, but Carnage decides to betray him and goes on rampage mode on a new island named Mythical Island.

What is Mythical Island?
It's an island that is filled with mystery. Legend has it that the island flows through the wind, and disappears after a month passes. The island is home to many gemstones, including the legendary Burst Stones! They are 8 mystical different colored rubies, shrouded in mystery, bringing great power to whoever obtains them. Legend has it that the stones were hidden when the people who lived on the island abused it's power, which caused the island to be put in a curse that had lasted for hundreds of years, causing the island inhabitants to suffer. Hundreds die in the span of the 11 months. The way to break the curse is to use the stones to fight evil. This will revert the user into a Burst Form. 8 of the stones are hidden throughout the island...

Due to the island's disappearances, the island is known for being ancient, being behind in modern technology. Although some modern cities were built, not many buildings cover the island, and is still filled with nature.