Hot Mobile is the ninth boss in Sonic & Knuckles when playing as Sonic and the twenty-second when playing as Sonic and Tails. The boss appears at the end of act 2 of the Lava Reef Zone.
Hot Mobile attacks from the distance
Just before the boss, Knuckles
knocks Sonic and Tails down a high staircase like platform where, in the distance, Dr. Robotnik
inside the Hot Mobile launches a set of homing missiles which destroy the platforms Sonic and Tails run across. After this, they reach a huge area flooded with lava where Dr. Robotnik waits in the Hot Mobile, submerged in the lava. The lava forms a slope towards the machine, which is covered in spikes, causing small platforms which Sonic and Tails are standing on to slide towards the machine and break apart. Also, Dr. Robotnik fires spiked bombs into the air which, as they slide with the platforms, cause damage to the Hot Mobile. As the machine is so heavily guarded, this is the only way to cause damage to it.