The Jet Mobile (ジェットモービル,Jettomōbiru?) 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 Mushroom Hill Zone after the weather-altering satellite attached to the top of it is destroyed by the player, forcing the boss to surface from being hidden in the ground and retreat with the player in pursuit.
Dr. Robotnik will not attack directly in this battle; the way of him "attacking" are the spiked ball hurdles which Sonic, Tails, or Knuckles must jump over or dodge. If they do so, they can get in close enough to use a Jump Attack against him, but they have to do so before the Jet Mobile quickly boosts backwards to avoid them. After landing eight hits, the Jet Mobile crashes into a large tree and falls off the screen as Sonic, Tails, or Knuckles pass through a hole underneath it to escape and get to the Capsule.
Defeating the Jet Mobile is by means of jumping and running. Sonic, Tails (lock-on only), or Knuckles must avoid the spike traps and the flames that it releases from its jet exhausts, and quickly attack after jumping over the spike traps before the Jet Mobile dodges out of the way. If the player stops running, their character will slowly scroll over to the left and be pushed along the edge of the screen due to the ground constantly moving. As usual, this boss is harder for Knuckles due to his lower speed and jumping abilities compared to Sonic and Tails.
A glitch sometimes occurs during Knuckles' story, causing Robotnik to be the pilot of the machine instead of the EggRobo. When defeated, it is shown crashing into a large tree, with a hole at the bottom of the tree just large enough for Sonic, Tails, or Knuckles to run through.
Oddly, whenever the Jet Mobile is damaged, the spiked ball hurtles are also seen taking damage- meaning that they also flash when the Jet Mobile itself is hit.