The Graviton Mobile (グラビトンモービル) is the fourth boss of Sonic the Hedgehog 3, fought at the end of Carnival Night Zone Act 2.
When Sonic and/or Tails get to the boss area, they will see Dr. Eggman fly in with the Graviton Mobile. He drops a green ball down at the player, then flies over above it and uses the power of electromagnetism around the ball. While he does this, the player will be pulled towards the electricity, so they must keep away from him while he does this. If the player has a Lightning Shield, they will be immune to the electricity, but they can still take damage from the ball. After Eggman finishes using the electricity, he will drop down to pick the ball up. When he does this, the player should start hitting him on the head to get a hit. Do this eight times to defeat him and finish the Zone. After popping the Capsule, Sonic or Tails jumps into one of the carnival cannons to be shot to the IceCap Zone.
"Wait a minute, I'm not supposed to challenge you..."
Knuckles does not have to face this boss in Carnival Night Zone, and his route to IceCap is somewhat different, hopping into a teleporter rather than the cannon. However, if he takes Sonic's route throughout this zone, he can climb up the shaft Sonic normally travels, and fight the boss (Eggrobo) optionally. This does lead to a bizarre transition between Zones.