The Shrimpy Truffle is a drop from the Duke Fishron Treasure Bag that drops on Expert Mode. Equipping and using this will summon a Cute Fishron Mount which will hover and fly infinitely and will obtain a speed boost once it touches water. A good strategy is to put bubbles with water purchased by the Party Girl NPC to get a massive speed boost in the air without having to dive in to water pools.
The Fishron Mount will also gain the speed bonus if you touch honey or lava.
The speed boost is also gained if the player riding it has half health or less.
When you get the liquid boost, the Fishron Mount's eyes will glow, and they glow with whatever color the water is in that biome. (eg. Pink in Hallow)