Doctor Robotnik’s Whirlpool Machine (ビッグシェイカー Biggusheikā?, lit. "Big Shaker") is the second sub-boss in Sonic the Hedgehog 3. It is encountered in the first act of Hydrocity Zone and takes six hits to be destroyed.
The sub-boss robot has a round-shaped body with red-metallic skin, and yellow lines in an X-formation on the center. The robot is also seen to have purple eyes. Its main weapons in the battle are thruster missiles that protect it from the player's attacks, as they're spinning around the body until it plants itself on the cylinder to use its whirlpool attack.
The Whirlpool Machine is fought in a bowl-shaped arena half-filled with water, which the player falls into after going around the downward guiding shuttle loop. Small missiles (which presumably are thrusters for the robot) orbit its central body acting as a shield as it charges down both sides of the arena. The player is unable to hit the robot without getting damaged during this time. After the Whirlpool Machine has charged twice, it settles down on the pole-shaped turbine in the middle of the arena, activating it to create a whirlpool underwater. This stirs up the water (and the playable character with it), rendering both the boss and the player unable to do anything until the stirring stops.
Hits can be scored either when the Whirlpool Machine begins to activate or stop the turbine pole's functionality. After starting up its thruster missiles again, the Whirlpool Machine starts repeating its attack pattern. Sonic can score the six hits needed to defeat this boss before the stirring starts for the first time with the help of a Water Shield. After this, the Whirlpool Machine will be destroyed along with the turbine pole itself. When the signpost falls down, two Super Ring monitors are hidden under the center part of the bottom arena, each of which have a small gap between each other.
This mini-boss, like all the ones from Sonic the Hedgehog 3, can be fought with Knuckles in Sonic the Hedgehog 3 & Knuckles. Most mid-bosses and major bosses are increased in difficulty for Knuckles. In this case, the attack pattern remains the same, but is made more difficult by Knuckles' reduced jump height. He can jump over it, but only barely. Knuckles is unable to jump high enough to get above the surface of the water so must Spin Dash up one of the sides of the arena periodically to prevent drowning.
The battle can also be made a lot easier for Knuckles, however. If Knuckles climbs up the right side wall above the water before the Whirlpool Machine begins its sweeping attack, and dodges that attack by gliding to the opposite wall twice, Knuckles can jump off the wall and bounce on the Whirlpool Machine from above for an easy kill while he is doing his whirlpool attack.
- In the standalone Sonic the Hedgehog 3, the major boss BGM will unusally play instead of the usual mid-boss theme for this boss battle. This is later fixed in the locked-on version of the game.
- An interesting glitch can also happen in standalone Sonic the Hedgehog 3 when the player stays on underwater until the drowning music starts playing and then jump out of the water. This time, the mid-boss music from Sonic & Knuckles will eventually start playing at the background. This glitch also works later in the boss battle with Screw Mobile, and will also work in the locked-on version.
- It is possible to drown while fighting this boss, as the thirty-second limit still applies, although it is not possible to drown while the score is being tallied or during the transition to the next act.
- In Sonic Mania, this mini-boss fight is referenced during the Laundro-Mobile's second phase.