Snufit Balls are projectiles used by Snufits. They are small black sphere which can be fired at a very high speed from the mouth of a Snufit.
In Wario & Geno: Saviour of the Stars, Snufit Balls are fired by Snufits both during the overworld and battle. Colliding with one on the overworld will start a battle against the Snufit Ball, similar to the Bullet Bills from Paper Mario. They can also be spawned during battles by Snufits.