Hammer Eggman, as the name implies, is a giant Eggmobile with two rocket-boosters on each side and a giant hammer. It is mostly grey with black and yellow stripes, and red stripes on the rocket-boosters. The hammer is mostly red with yellow and blue stripes.
Dr. Robotnik will raise up two totem poles and fly around the top with his giant hammer. He will hit the tops of each totem pole, and one of four heads will shoot an arrow out of its mouth (sort of resembling the statues that spit poison in Labyrinth Zone). This usually gives the player a chance to get on top of the totem poles, and hit Robotnik freely. As with every Eggmobile in Sonic the Hedgehog 2, Tonkachi Eggman takes eight hits to be defeated.
- This boss battle is referenced in Sonic the Hedgehog 4: Episode 2 in the boss battle of Sylvania Castle Zone. At the start of the battle, the pillars from the original battle appear to trick the player into thinking they are going to fight a remake of the Tonkachi Eggman boss. Instead, the pillars are destroyed, revealing the true boss, the Egg Serpentleaf.