This is a kinetic display stand for the shark from LEGO set 31088 Deep Sea Creatures. Turning the crank on the side of the model causes the shark to ‘swim’ while opening and closing its mouth. It also has a place to display the crab and treasure chest that come in the set.
Here's a short demonstration video where you can see it in operation.
There are two versions of the kit available, depending on if you already own set 31088.
Stand Only
Full Model
Motor option
Build Notes
Note that in addition to building the stand, several changes need to be made to the shark itself. This involves replacing all of the body joints, and the lower jaw hinge, so they all move freely.
If you already have the shark built, you will need to partially disassemble and modify it. The parts and instructions for doing this are included with both versions of the kit.