As the name states, Ghost Whale is a giant, robotic whale. It has several hues of purple on its sides, back, and tail. It has a giant red jewel on its head, tan teeth, and green eyes. It has light-purple wheels on its side and peach colored stripes most of the places. It has yellow blowholes on its back.
The inside of Ghost Whale has several shades of green and has mostly water on the floor (due to it being on the ocean). Red wires are also inside the robot.
After Sonic, Tails, Blaze, and Marine find Captain Whisker, they find that the Vikings were frozen solid, and Captain Whisker sends the Ghost Whale to attack Sonic (or Blaze) and freeze them just like the Vikings.
In the first part of the battle, the block of ice Sonic or Blaze stand on serves as a platform. The Ghost Whale swims towards the platform from the right while spawning smaller robotic fish to try to distract the player. The Ghost Whale will bite a chunk off the platform from the edge so the player will need to stand away from there to avoid damage. The Ghost Whale will then become dazed from the impact, allowing the player to hits its exposed jewel on its forehead with a Spin Jump/Axel Jump.
A small cutscene plays showing the player's character entering the Ghost Whale's mouth. In the second part of the battle the player must navigate through a short platforming obstacle section inside the Ghost Whale within a time limit of 30 seconds. The player must then navigate through the Ghost Whale to find the "heart". Along the way, the Ghost Whale will use its internal defenses, such other robots, missiles (which double as platforms), ice patches or pools that freeze the characters to slow down the player. If the timer expires, the Ghost Whale will expel the player out. By destroying grey nodes inside the Ghost Whale, the timer gets restored back to 30 seconds.
Once the heart is found, the player must attack it, and the Ghost Whale will sprout the player out through his blowhole. This process must be repeated twice. Each time the player enters the Ghost Whale, the platforming section to the "heart" becomes slightly harder, with a different layout. Also, each time the Ghost Whale spits out the player, it smashes a section of the ice platform that the characters stand on; if the boss is not defeated before the entire ice floe is destroyed, then the player loses a life. After three hits, the Ghost Whale will be immobilized until the player jumps to hit the jewel on his forehead one last time. After that hit, he will explode.
On normal difficulty, the fish-like robots that spawn in the ice floe section come in groups of three and two (for last phase) as opposed to two and one (last phase). There are less time bonus nodes inside the Ghost Whale as well.