Fireball 3 is indoor level, that takes place in a cave, one must jump across the platforms floating in the water/lava to make it through the level, while avoiding boulders. It is the Third level on the Fireball Level Path, in Dark Castle. It has shown up in Dark Castle, and Color Dark Castle, and will show up in Return to Dark Castle.
It is unknown what liquid will be in Return to Dark Castle.
This is the same liquid in Fireball 2.
Levels on the Path
Main article: Fireball Level Path