Mortar Canyon is the twenty-second stage of Sonic Forces and the seventh stage to be played by Modern Sonic. The stage itself takes place inside the Eggman Empire Fortress and encompasses the route leading from the edge of the fortress to its Central Tower.
Having been saved from annihilation by a virtual sun, the Resistance gains a morale boost and continues fighting against the Eggman Empire. Meanwhile, Tails detects that Infinite's Phantom Ruby must have been weakened from forming that sun and sees this as the Resistance's one chance of finishing him off. This prompts Sonic to chase after Infinite, while Knuckles commands all of the Resistance ships to attack and take as much fire-power off of Sonic as possible. Eventually though, the Resistance ships are forced to retreat by the Eggman Fleet, but by the time that happens, Sonic has already reached the Central Tower.
Mortar Canyon tests the player's platforming skills with Modern Sonic. Throughout the stage are small platforms and narrow paths, all suspended over bottomless pits (which are marked with red laser grids); one mistake here will lead Sonic to his end. The stage also has several strings of Nebulas in midair for the player to skip across (and thereby cross gaps) using the Homing Attack.