A Float Stone is a held item that halves the holder's weight. It can be crafted, and can also be obtained as a tier 1 special drop. It is also a drop from certain wild Pokémon.

What does a float Stone do?

The Float Stone is a hold item in Generation V, given by a man inside Drayden's house in Opelucid City. It's a very light stone which halves the weight of the Pokémon holding it. This reduces the damage taken by weight-based attacks such as Grass Knot and Low Kick.

Does the float stone increase speed?

In Pokémon UNITE, the Float Stone increases the equipped Pokémon's Attack by 24 and Speed by 120, and increases their movement speed while out of combat.