Minecraft Dungeons:Clam

The Clam is a mechanic added in the Hidden Depths DLC which acts as the underwater equivalent of the Piston Launchpads seen in the Obsidian Pinnacle, ???, Overgrown Temple, Frosted Fjord, Lost Settlement, camp, and the Gale Sanctum, used to launch players up high platforms.

Behavior
When any mob or the player is near, the Clam would shake. After a few seconds of uninterrupted contact with the clam, it will launch the mob or player up a height and then close down.