The unnamed final boss is the sixth and final boss fought in Sonic Blast. This boss can only be fought if all five Chaos Emeralds have been collected before defeating the previous boss.
After the destruction of the previous boss' arena, the player will be warped to a new arena, retaining all the Rings they had in the previous fight. The true final boss, an egg-shaped robot with a screen controlled by Dr. Eggman will activate and separate itself into two halves that activate their sawblades, with the upper half floating above the arena.
The top half moves left and right across the screen, attacking the player by dropping blue energy balls directly downward. Not only must the player avoid touching them, but the sawblades on the flat sides of both halves will also cause damage. To attack the boss, the player must stand on top of the bottom half of the boss, which will make the top half stop and display an arrow pointing at the robot's weak spot on its screen. At this point, the player must jump up and hit the boss from the top before the screen switches back to Eggman to damage the boss. If the player attacks the weak spot while Eggman is shown on the screen, the player's attack will just bounce off without causing any damage. Reaching the weak spot is also made more difficult by the boss sporting drill horns that will cause damage if the player lands on them by mistake. Sonic has an easier time avoiding these drill horns than Knuckles thanks to his Double Jump. Each time the boss is successfully hit, it will retaliate by moving to the middle of the screen and dropping four energy balls at once.
After six hits, the bottom half of the boss will start moving independently from the top half, making it more difficult to attack the weak spot. After six more hits, the boss is defeated, and the player will be presented with the good ending where the Silver Castle Zone sinks into the ocean by the shores of South Island, with Sonic or Knuckles holding the Chaos Emeralds as he watches the fortress' destruction.