The Shiny Red Balloon is an accessory that increases the player's jump height from 12 feet (6 blocks) to 21 feet (10½ blocks). However, it reduces underwater jump height by one block. It can be found in Chests on Floating Islands. It can also be obtained from Sky Crates.
The Shiny Red Balloon stacks with other jump-boosting accessories:
With the Frog Leg, jump height is increased more than with either accessory alone. A single jump with Frog Leg and Shiny Red Balloon reaches 33 feet (16½ blocks).
With the Cloud in a Bottle, double-jump height is increased from 9 feet (4½ blocks) to 17 feet (8½ blocks), for a total jump of 38 feet (19 blocks).
With the Blizzard in a Bottle, double-jump height is increased from 16 feet (8 blocks) to 29 feet (14½ blocks), for a total jump of 50 feet (25 blocks).
With the Sandstorm in a Bottle, double-jump height is increased from 28 feet (14 blocks) to 52 feet (26 blocks), for a total jump of 72 feet (36 blocks).
With the Tsunami in a Bottle, double-jump height is increased from 14 feet (7 blocks) to 26 feet (13 blocks), for a total jump of 46 feet (23 blocks).
With the Rocket/Spectre Boots, flight is accelerated, making the same flight time carry the player higher and/or farther.