Power Stone

Power Stone (パワーストーン) is Stone Man's Special Weapon. When used by Mega Man in Mega Man 5, 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).

Power Stone is Charge Man's weakness, inflicting four units of damage against him.

In Mega Man 2: The Power Fighters, the Power Stone launches a giant stone hand that rises from the ground and moves forward.

The Power Stone is also used by the "Bridge" in Mega Man IV.

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.

Bosses weak against Power Stone

 * Mega Man 5: Charge Man, Dark Man 4
 * Mega Man IV: Charge Man, Ballade
 * Mega Man (Game Gear): Star Man
 * Mega Man 2: The Power Fighters: Elec Man

Other media
Mega Man uses the Power Stone in the Mega Man animated series.

It also appears in Mega Man: Upon a Star, where Mega Man uses it against Samurai Man.

Trivia

 * Coincidentally, Capcom has a fighting game series called Power Stone.
 * Because it barely hits anything, most players tend not to use it, finding it one of--if not the--most useless weapon in Mega Man history.