South Island is an island on Mobius.
- South Island was the main setting for both versions of the video game Sonic the Hedgehog for Genesis and the Master System/Gamegear, alongside the 8 bit version of Sonic the Hedgehog 2, Sonic Chaos, Sonic Triple Trouble, Sonic Adventure 2, Sonic Battle, and the Sonic Advance trilogy.
- In Japan, according to the story for the Genesis video game Sonic the Hedgehog, South Island can't be found on any map, nor is it set in one location. It moves across the sea, possibly as a result of the Chaos Emeralds. Whether or not this information applies in the Pre-Super Genesis Wave Timeline (or even in the "modern" Sonic video games) is currently unknown.
- The locales of South Island appeared in the version of reality created by the first Genesis Wave (StH#226-#227). Whether or not these locations were also located on South Island in this reality is unconfirmed.