This section temporarily contains information copied directly from Bulbapedia, and needs to be rewritten so not to be classified as plagiarism.
“A Sandygast emerges when the grudges of Pokémon and other creatures soak into the sand after they fall in battle. In essence, it’s a possessed lump of sand! If you heedlessly grab a Sandygast’s shovel, you’ll fall under the Pokémon’s control. A Sandygast uses its power to manipulate children into gathering sand to increase the size of its body. If a Sandygast loses its shovel, it may put up a tree branch, a flag, or another item in its place. These Sandygast are wanderers in search of their own shovels. The tunnel-like mouth of a Sandygast can suck the vitality from people and Pokémon. Apparently it’s a test of courage in the Alola region to put your hand in a Sandygast’s mouth. Sandygast has the new Water Compaction Ability, an Ability that no previous Pokémon has had. With Water Compaction, its Defense stat will go up by 2 if it’s hit with a Water-type move.”
Sandygast is a Pokémon formed from sand. It is mostly a mound of whitish sand dotted with gray pebbles. A tunnel through its center acts as a mouth, and a small depression above that has two pebbles for eyes. A red shovel with a white handle is stuck blade first into the top of its head. On either side of its main body is a smaller mound reminiscent of a stubby arm.
Sandygast is born from grudges that seep into the sand, such as from Pokémon that suffer defeat in battle. It can suck the life force of people or Pokémon through its mouth. Apparently, in the Alola region, sticking a hand into Sandygast's mouth is a way of proving one's courage. A person who grabs Sandygast's shovel falls under its control. It uses this power to make children add sand to its body so it can become bigger. A Sandygast that loses its shovel may replace it with something like a branch or a flag, but it is said to keep searching for its lost shovel.