Sonic and Werehog have different abilities and weaknesses: Sonic is faster but weaker, whereas Werehog is stronger but slower. During the day, players play as Sonic, and when night comes, Sonic turns into Werehog. A level can take place at day or night (or both).

Players take control of either Sonic or Werehog in each level, battling enemies and collecting rings or other items while trying to reach the goal. With this ability and Chip's guidance, Sonic must travel around the world to stop Dr.Eggman, find shrines that fixes the Emeralds, and defeat Dark Gaia - a beast unleashed from Eggman's new weapon. What Eggman doesn't know is that the ray also gives Sonic the ability to turn into a beast called 'Werehog' at night. Sonic calls him 'Chip' and promises to get his memory back. When Sonic wakes up, he finds a little creature who apparently has lost his memory. Seeing that Sonic is now useless to him, he jettisons him and quickly gets away. He then drains the power of the Chao Emeralds from Super Sonic and use the power to create a blast strong enough to shatter the Earth into pieces.

During a battle with Sonic (in Super Sonic form), Dr.Eggman uses his new weapon and manages to trap Sonic.

Sonic unleashed java