Balloon Pufferfish

The Balloon Pufferfish is an accessory that increases the player's jump height by 33% and jump speed by 30%, increasing the height that the player can jump from 6 blocks (12 feet) to ~10½ blocks (21 feet), effectively a ~75% boost; however, it oddly reduces jump height when underwater, from 8 blocks (16 feet) to 7 blocks (14 feet), meaning it grants the same jump height bonus and downside as the Shiny Red Balloon. It can be obtained via fishing in any biome.

Trivia

 * Despite being functionally identical to the Shiny Red Balloon, the Balloon Pufferfish can only be tinkered with one double-jump accessory: the Tsunami in a Bottle. Conversely, the Shiny Red Balloon can be tinkered with every double-jump accessory except for the Tsunami in a Bottle.