From WiKirby, your independent source of Kirby knowledge.
Stone-Stone is a Power Combo of two Stone abilities in Kirby 64: The Crystal Shards. It is more or less identical to Stone, but it causes Kirby to grow in size.
When used, Kirby becomes a giant stone and falls to the ground, rolling a short distance if Kirby was moving horizontally at the time. From here, the stone can form into a giant stone replica of Kirby and walk around, damaging any enemy he touches. When reaching a hill, Kirby will assume regular stone form again and roll down it. When transforming back, the stone bursts, which can also damage enemies.
If Kirby touches a Gordo or another invulnerable obstacle while in Stone-Stone form, he bounces off it and reverts to normal without taking damage in the process.
Like the other abilities in Kirby 64: The Crystal Shards, this ability does not change Kirby's physical appearance in any way until it is used.