Power Stone

Power Stone (パワーストーン) is Stone Man's Special Weapon. In most appearances it releases three stones that spiral about by using the force of attraction on each other to crush enemies with their circumferential orbit. In Mega Man 2: The Power Fighters it summons a large stone hand from the ground.

Mega Man 5
Power Stone is obtained by Mega Man after defeating Stone Man. When used by Mega Man, three stones shoot out and spiral about. It can be helpful to take out enemies in hard to reach (or dangerous) spots, such as the Power Muscler in the second area of Wily Castle (near the boss, Circring Q9). Charge Man and Dark Man 4 are weak to this weapon, although Charge Man is immune to it when shooting his coal or performing his Charge Kick.

Mega Man IV
Power Stone is Charge Man's weakness, inflicting four units of damage against him. It is also effective against Ballade.

The Power Stone is also used by the "Bridge" boss in the Wily Battleship.

Mega Man 2: The Power Fighters
Unlike other appearances, the Power Stone launches a giant stone hand that rises from the ground and moves forward a short distance in front of the user before returning to the ground. Up to two hands can be on the screen. It is Elec Man's weakness, and also does good damage on Cut Man, Dive Man, and Slash Man.

Mega Man (Game Gear)
Power Stone is Star Man's weakness.

Damage Data Chart
Damage values in units in Mega Man 5.

Capacity
In Mega Man 5 and Mega Man IV, each use of Power Stone only drains one weapon energy unit. With a full weapon energy gauge, it's possible to use Power Stone twenty-eight times in Mega Man 5 and 19 times in Mega Man IV.

Mega Man (Ruby-Spears)
Mega Man uses the Power Stone in the Mega Man animated series episode "The Big Shake". The Power Stone is used in a more straightforward manner in the cartoon, fired as a projectile from Stone Man's and Mega Man's arm cannon.

Mega Man: Upon a Star
Mega Man uses Power Stone against Samurai Man.

Mega Man Megamix
In Stone Man's profile, the Power Stone is said to cause extremely dense stones to hit an opponent while swinging around the user's body, accelerated by each other's gravitational pull. In the story, the only time the weapon is used is as part of the combined attack from the Hourly Pay Squad: Part-Timers. After Gravity Man sends the opponent up with Gravity Hold, Stone Man and Gyro Man launch a joint attack, Stone Man using a "Power Stone Special Edition" (パワーストーン特別編) that consists of him taking a large stone with both hands and hitting it on the opponent's head.

Trivia

 * Coincidentally, Capcom has a fighting game series called Power Stone.