The Self D-Struct Machine (ボウリングスピン,Bouringusupin?, lit. "Bowling Spin"), or the D-Struct Machine for short, is a sub-boss that appears in Sonic the Hedgehog 3. It is encountered in the end of Carnival Night Zone Act 1, and must hit itself four times to be defeated.
The D-Struct Machine is hovering mecha created by Dr. Robotnik that has green and grey colored metallic skin, and small lamps on the top. It also has a spinning top attachment below, that functions as a floating platform with a set of spikes spinning on its border.
The D-Struct Machine is encountered in an elevator room with a floor made of yellow-and-green blocks that descend down a vertical tunnel. After landing in the arena, the D-Struct Machine releases its twirling spike-covered top that will bounce around the room and destroy the yellow-and-green blocks on the floor upon contact with them. The rest of the mecha will hover from side to side constantly, and will only stop when hit by the player. The spinning top also acts as a platform, while the player must avoid the bottom part and the spikes on the platform.
The player has limited time to defeat the D-Struct Machine, as the spinning top will eventually destroy the whole floor, leaving the player to fall to their death. To compensate for the limited time, the D-Struct Machine is weaker than the other mini-bosses in the game and only has to be struck four times rather than six to be destroyed. However, the player cannot damage the D-Struct Machine directly. After hitting the D-Struct Machine once, the tube on its bottom will extend and surround itself with an electric field that will hurt the player if they touch it. At this point, the player must let the spinning top bounce back into it.
After the D-Struct Machine has been defeated by hitting it four times, the arena floor will reach the bottom of the vertical tunnel and the signpost will drop from the top of the screen. At this point, Sonic can fall down through any gaps that may have opened up in the floor at this point or be crushed by the rest of the blocks that are coming down due to the D-Struct Machine leaving uneven holes between the blocks.
Knuckles' battle against the D-Struct Machine is identical in Sonic the Hedgehog 3 & Knuckles. However, in this version, Knuckles enters to the elevator from his own pathway in the Zone. During the battle, Knuckles is unable to climb on the elevator room's walls and, depending how long the battle lasts, the player may need to use the D-Struct Machine's spinning top to reach the D-Struct Machine in order to hit it due Knuckles' low jumping height.
Strangely, a Lightning Shield does not protect the character from hitting the electric field that forms around the tube on the bottom of the boss (the shield is lost as soon as such a hit is sustained).
Spin Jumping up into the Spinning Top from below forces it upwards.