Facts:

A Clam, also known as a Clam Launcher, is a mob-like mechanic added in the Hidden Depths DLC which acts as the underwater equivalent of the Piston Launchpads seen atop the Obsidian Pinnacle, on Mooshroom Island, in the Overgrown Temple, Frosted Fjord, the Lost Settlement, the Gale Sanctum, and the camp, used to launch heroes up high platforms.

Behavior:

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

More facts here: https://minecraft.fandom.com/wiki/Minecraft_Dungeons:Clam

Difficulty: very easy

How long it takes: about 30+ minutes