Unknown (アンノウン An'nōn?), also called F-Zone or Point-W on the Zone Map, is the eighth Zone in Sonic Rush, and the final Zone of both Sonic and Blaze's stories. It is the first final boss battle of the game, followed by Exception. The theme for Unknown is "Bomber Barbara". The only event that occurs here is the final battle against Dr. Eggman or Doctor Eggman Nega in the Egg King.
The battle takes place on a piece of scrap metal that probably came from Dead Line as it hurtles through the Earth's atmosphere. At first, it will remain in the background and attempt to pound Sonic or Blaze with its fists, which release shock-waves, or fire a laser which leaves behind a brief fire trail. Eventually, it will move to the right side of the ship and attack similarly there. After several shock-waves, the fist stops moving and the player can hit it, immobilizing it and allowing them to run up and hit the cockpit. An on-screen prompt lets the player know when to duck to avoid being shaken off at certain points.
After four hits, the mech changes its pattern and includes a new move. It can release a probe that hovers over the player and unleashes electrical bolts that must be stayed between until it disappears. Once it disappears, the mech will move to the side again to allow the player to attack it. Sometimes, the mech will hit the platform in multiple succession causing many shock-waves that the player must jump over (easier with Blaze and her Hover Burst). When the player jumps over all of them and doesn't get hit, the mech will go to the side, giving the player a chance to damage it. If you get hit, then you either start over or he'll do another attack.
On its final bar of health, Eggman will launch a kamikaze attack and try to destroy the battleship by ramming it. There's nothing the player can do until the third hit, where it will remain in place. The player can then launch the final hit and destroy the robot.
In Sonic's story, after defeating Eggman Nega, he comments that it "was easy" and Tails and some small animals join him, Knuckles then appears saying that "I think you should split now." because Amy appears and chases after Sonic. Tails then comments that "At least everything is back to normal". Finally, the credits play as Sonic is running away from Amy. After the credits, Sonic has a shocked look and performs a desperate spin dash and speeds off the screen, followed by Amy running after him with a mallet. (Similar to the one she gets when paired with Knuckles in Sonic Advance 3.) If the player hasn't collected all the Chaos Emeralds, Eggman Nega will appear with a message: "Collect all the Chaos Emeralds." If the player has all the Emeralds, but hasn't finished Blaze's story, Nega will tell the player to finish Blaze's story.
In Blaze's story, after defeating Eggman, she looks among the wreckage to find Cream. When it seemed that the worst had happened, Cream falls out of the sky and thanks Blaze for rescuing her. Blaze then states that it's because they're friends. The credits roll with simply Blaze and Cream walking while Cheese performs various actions like spinning. After the credits, Blaze is ahead of Cream and stops walking so she can catch up, after Cream does, she looks up at Blaze. If the player has completed Blaze's story and not Sonic's, Eggman will tell the player to finish Sonic's story and collect the Chaos Emeralds.
- The background music for Unknown, "Bomber Barbara," has parts that are derived from "Teknopathetic," a song from Jet Set Radio Future in the Jet Set Radio series, another highly praised Sega franchise. This is probably due to the fact that both games' soundtracks were written by Sega composer Hideki Naganuma.
- Point-W and F-Zone could be a cross-reference, as Sonic can utilize the power of the wind and Blaze has control of fire.
- The colors on Eggman's mecha correspond to Blaze's color scheme (purple-ish pink), while the colors on Eggman Nega's mecha correspond to Sonic's color scheme (red, white, and blue).