Null Space starts out in a dimension of nothingness, but soon transitions into a war-torn Metropolis. During the events of the game, Dr. Eggman banished Sonic to null space in an effort to dispose of him for good. However, with the aid of the Avatar, Sonic was able to return to Metropolis, just as the Resistance was about to take the city.
The introduction to the stage takes place in "null space" (虚無空間 kyomu kūkan?), a supposedly inescapable, closed-off pocket dimension created by the Phantom Ruby where nothing exists. This dimension is a purple void with floating cubes and net-like grids above and below that extend into infinity. The only solid ground here is a road made up of purple cubes with lightning swirling around it.
The rest of Null Space takes place within Metropolis, which appears as a magnificent and pristine, but sterile white city where geometric shapes appear to be a recurring architectural theme. It features multiple skyscrapers in various designs, numerous large-scale video screens, and open, see-through highways, all of which look like they are taken straight out of the future. Various buildings with advanced technology fill the city as well. In addition, the sky above Metropolis is free of pollution; instead, it is blue with a couple of clouds dotting it.
Resistance airships can be seen engaging the Eggman Fleet in the sky above Metropolis while fireballs rain from the sky, destroying buildings. Black smoke columns can likewise be seen in multiple places around the city, due to damage from the Resistance as they lay siege to the city. Also, at the end of stage is a massive alien tower with several spheres attached to it, and gate-like rings on top.
The bottom of Metropolis is not visible; the entire ground level below the skyscrapers is obscured from view by a thick cloud cover. Also, Metropolis has no traces of organic nature.
Having been trapped in Null Space by Infinite to show that the Death Egg's destruction did not weaken the power of Infinite's Phantom Ruby prototype, Sonic and the Avatar decide to break out. Using the Double Boost, the two of them are able to force their way out of Null Space and return to a Metropolis under heavy siege by the Resistance. Surprising Knuckles over the radio with their sudden reappearance, Sonic and the Avatar resume their hunt for Dr. Eggman.
While Sonic and the Avatar make their way through the city, Amy gives them an update on the battle in Metropolis, revealing that the Resistance's fleet has gained the upper hand over the Eggman Fleet and that they should have everything under control if all goes well; Rouge herself urges Sonic to hurry, as he is missing all the fun. Soon after, Sonic and the Avatar find Eggman, his henchmen, and Infinite. Although shocked to see that Sonic has escaped the inescapable Null Space, Eggman refuses to give up just yet, and warns Sonic that he will have the last laugh before retreating in the Egg Mobile, with his henchmen following him, essentially abandoning Metropolis, leaving it to be captured by the Resistance at long last.
Null Space takes place almost entirely in 3D. There are many alternative routes and hidden Grind Rails here. Rails allow the player to avoid most fights with opponents. However, on the roofs the player will usually have to first defeat a group of enemies to move on. In such cases, a Pulley will sometimes reveal itself after all the enemies have been cleared out
Like in other Tag stages, the player controls both Sonic the Hedgehog and the Avatar at the same time here, with the lead character switching to Sonic when Boosting and to the Avatar when using the Wispon. To accommodate the different characters, the stage has mechanics for both of them. For Sonic, the stage has Wisp Capsules with White Wisps along the way so the player can charge their Boost Gauge. For the Avatar, the stage has Wisp Capsules with miscellaneous Wisps for fueling the Avatar's different Wispons. However, any Wisp Capsule containing Wisps that do not match any of the Wispons the player has currently obtained will be rendered intangible and transparent until the player obtains their Wisp's associated Wispon. This means, for example, that if the player does not have a Lightning Wispon, then the capsules with Ivory Wisps will be unobtainable.
When the stage begins, the player is stuck running on a road in Null Space. Soon after starting the stage though, the player is prompted to activate the Double Boost, which will allow them to boost through obstacles and escape from Null Space.
Upon emerging into Metropolis, the player will be led to the top of a building with a pair of Star Posts on it. There, the player can board a Grind Rail. By following it, the player will find at a number of branching paths; some will lead from rail to rail, others can take the player through midair and Dash Ring/Rainbow Rings, others will remerge with different paths, and others still will take the player across rooftops where they have to take out waves of enemies to proceed.
Except for one, the alternate routes will eventually join together and lead to some rooftops with a pair of Star Posts on them before branching out again. All of these paths will later join together again on final stretch leading up to the tower at the end of the stage though. The final section here consists of square platforms that must be climbed. On each of them, the player will be confronted by waves of enemies. On the first one, the player has to take out all the enemies to make a Pulley reveal itself. On the second platform though, the player can skip the enemies and just use a Spring. After that, the player will reach the platform with the goal, which has Eggman and Infinite standing next to it.
- Unused dialogue from Sonic suggests that the portion of the stage that takes place in Null Space was meant to go on for much longer.
- Concept art for the level indicated that Infinite would have appeared at some point in the level, or at the very least his likeness.
|"Null Space"||Tomoya Ohtani, Yutaka Minobe||1:57|
|"Fist Bump - Escape from Null Space"||Douglas Robb||1:26|
- Sonic Team (November 7, 2017). Sonic Forces. Nintendo Switch. Area/Level: Metropolitan Highway. "Dr. Eggman: Har-har. That, my spiky little frenemy, is null space. / Sonic: Null space? / "Dr. Eggman: It's a little something that the Phantom Ruby cooked up, a closed-off space where absolutely nothing exists!"
- Sonic Team (November 7, 2017). Sonic Forces. Nintendo Switch. Area/Level: Null Space. "Dr. Eggman: What?! It can't be! It's impossible to get out the Phantom Ruby's null space!! / Sonic: Maybe by myself, but I had a little help from my friend. Something you wouldn't understand, since you don't have any friends!"
- Sonic Forces PC - Null Space Once a Full Stage? (Unused Dialog). YouTube. codenamegamma (19 November 2017). Retrieved on 6 October 2017.