Spark Shock

Spark Shock (スパークショック) is Spark Man's special weapon. This weapon basically shoots sparks, as the name implies. Some enemies merely get paralyzed when hit, but a few enemies like Magnet Man can be damaged by this weapon. It's downside is only two enemies can be stunned at a time and you cannot change your weapon while there's one stunned.

However,they changed this in Mega Man III,allowing you to stun enemies,and still being able to switch weapons.In some cases,this comes very handy when dealing with Shield Attackers

Capacity
Spark Shock uses one weapon energy unit in Mega Man 3 and Mega Man III. With a full weapon energy gauge, it can be used 28 times in Mega Man 3 and 19 times in Mega Man III.

Bosses weak against Spark Shock

 * Mega Man 3: Magnet Man, Doc Robot (Air Man and Bubble Man), Spark Man (2nd Encounter), Wily Machine No. 3 (1st Form)
 * Mega Man III: Snake Man, Giant Suzy
 * Mega Man: The Wily Wars: Iron Ball, Wily Machine (1st Form)
 * Super Adventure Rockman: Ra Thor

Bosses immune to Spark Shock

 * Mega Man 3: Needle Man, Hard Man, Doc Robot (Flash Man), Yellow Devil Mark 2, Holograph Mega Men, Gamma
 * Mega Man III: Dive Man, Drill Man, Skull Man, Punk, Wily Machine
 * Mega Man: The Wily Wars: Buster Rod. G, Wily Machine (2st Form)

Other media
Mega Man uses the Spark Shock and Gyro Attack at the same time in episode 8 of the Mega Man animated series. When obtaining the weapon, an electrode can be seen in its design, probably for firing the sparks.