Egg Liner is a vehicle with Eggman Nega (who is disguised as Dr. Eggman) sitting in the cockpit which is located in the front of the vehicle. It is mostly red with a yellow bumper that holds a spiked ball (which is orange and has yellow lines where the spikes are) in the front. It has several gray exhaust fumes on the back, black and tan lines around the circular windows, and black wheels.
Eggman Nega will prepare for an attack by raising the spiky ball leaving the front exposed, when he does this, the player must knock back their rival and strike it before it can launch its attack. The Egg Liner will also move the ball diagonally preparing to attack straight forward which must be avoided by jumping over it. The player has to hit the vehicle a total of six times in order to defeat it. Once defeated, the contraption will be blown up, leaving Eggman Nega to escape in his Egg Mobile.
- This boss is similar to EggHammerTankII from Sonic Advance 2. Both of the battles feature Auto Running and are the first bosses of their respective games.