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". It serves as the stage containing the penultimate battle against Dr. Eggman or Doctor Eggman Nega in the Egg King.
While Unknown is set on a metal platform in outer space (possibly a piece of scrap metal that came from the destroyed Dead Line, the background continually changes based on the player's progress throughout the battle as the platform descends closer to the Earth's atomsphere. At the beginning, the moon is visible in the background and at the end, the Earth can be seen.
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 fighting Sonic and coming to good terms with him, Tails alerts Blaze with a letter from Dr. Eggman announcing that he kidnapped Cream and would only return her if Blaze came to Point W alone. Although Sonic and Tails wanted to help Blaze rescue Cream, Blaze insisted that she could accomplish this on her own due to her friendship with Cream.
After defeating Eggman, she searches 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 is because they are 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 boss of Unknown, and the only playable section of this stage, is the Egg King, a behemoth of a robot piloted by Eggman and Eggman Nega respectively. It can be fought immediately after entering Unknown.
In battle, the Egg King attacks with shockwave-inducing slams, laser beams and drones. To damage the Egg King, the player must attack its fists or head when they are accessible. In the latter case, the player must climb the Egg King's arms to reach its head. As the battle progresses, however, its attacks get more relentless. After enough hits, the Egg King will try three last attacks which must be dodged before hitting its head for the last time.
- 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).