The core mechanics of Duality in similar to Asteriods, in which the player must control a ship in a 2-D space while obstacles approach the ship; the ship is capable of firing ammunition and activating its rocket boaster for propulsion, both at the cost of energy represented by a green bar (which will refill after a short time without use), while also featuring a red bar to indicate the ship's health.
As opposed to simply destroying approaching objects, gameplay in Duality is centered around the concept of attaining "Black" (negative) or "White" (positive) points, represented by small and large spheres colored black and white that the player's ship may encounter:
- The large spheres have their own gravitational pull that affect movement of the player's ship; white spheres pull the player away while black ones pull the player towards them. If the ship touched a large black sphere, the ship's health will deplete and eventually result in the ship exploding, ending the game. The player may shoot any large sphere destroying a black one will award the player 10 "white" points while destroying a white one will award the player with 10 "black" points.
- The smaller spheres are actually indestructible pickups that replenish the ship's energy bar, but their effect on the player's score varies between black and white. Contact with a white sphere will award the player 5 "white" points, while black ones award the player 5 "black" points.
Regardless of whether the player has a black or white score, the player will lose one (black or white) point for each bullet shot, thus requiring the player employ some degree of precision to maintain their score count.
With these rules in mind, the player can choose to aim for a high "white" score or a high "black" score, each presenting slightly different challenges to the player. It is also for this reason that the game keeps tabs for both the 10 highest "white" scores and the 10 highest "black" scores, the only minigame in the GTA series to have two hi-score lists.