Thunder Wool

Thunder Wool (サンダーウール) is Sheep Man's special weapon. Mega Man launches a thunder cloud that slowly rises, and a lightning bolt shoots straight down from the cloud. He can fire up to two consecutive shots. The cloud itself does very minimal damage. Pairing two clouds together will increase the lightning strike area and power. Thunder Wool is Pump Man's primary weakness -- a single bolt from this weapon can dissipate his Water Shield.

Bosses weak against Thunder Wool

 * Pump Man: Mega Man 10
 * Weapons Archive/Tornado Man: Mega Man 10
 * It also does considerable damage against Crab Puncher and Block Devil

Trivia
The Thunder Wool is considered one of the worst Special Weapons in Mega Man history by some fans. Its high energy cost does not account for the area and power of the cloud and lightning strike.