The Hot Mobile (ホットモービル,Hot Mobile?) is a boss from Sonic & Knuckles, as well as its locked-on form, Sonic the Hedgehog 3 & Knuckles. It is fought in the second act of Lava Reef Zone.
The objective of the entire level is simply to dodge obstacles and not touch Robotnik. If the player does not have a Flame Shield, he/she must land on platforms and not touch the lava. Robotnik will shoot mines, so the player must be aware to dodge them. Robotnik will tilt the lava in a diagonal arc and hope to drag the player into touching the boss. Unfortunately for Robotnik, due to tilting the lava, the mines will also land on him, damaging his own vehicle.
Because this boss cannot be damaged by the player, this can be considered the longest fight in the game when attempting a speed run.
The Hot Mobile is the only main boss in the game that cannot be hurt by Sonic or Tails by any means; not even Super Sonic, Hyper Sonic, or Super Tails can damage it.