The Cloud in a Bottle is an accessory that allows the player to perform double jumps by hitting the jump key again in midair. It will also allow the player to perform a jump while falling, even if the fall did not result from a jump, making it one way to avoid fall damage. A "cloud jump" offers an additional jump of 3.5 blocks, for a combined jump height of 9.5 blocks. Its effect does not stack (ie. two bottles will not allow two extra jumps).
Rocket Boots stack with this item, allowing for a triple jump; the first double-jump activates the Cloud in a Bottle, and the second activates the Rocket Boots. Once you find the Rocket Boots, the Cloud in a Bottle becomes a lot less useful. Most players will then switch it for a more useful item, such as the Feral Claws or Anklet of the Wind.
The Shiny Red Balloon affects the double jump height of Cloud in a Bottle, increasing it from 3.5 blocks (7 feet) to 7 blocks (14 feet), for a grand total of 17.5 blocks (35 feet, including the initial jump).
If the Flippers are equipped and the player performs multi-jumps underwater, the player will not be able to perform a double jump upon exiting the water as the multi-jumps performed underwater count as a double jump (even though the double jump animations and sound effects are never shown).
When you are falling from a huge height, right before you hit the ground, double jump and you'll fall and hit the ground without taking any damage.
Its Quality is 1 (Blue) as of version 1.0.4 (3 (Orange) in earlier versions).