Time Stopper

Time Stopper (タイムストッパー) is Flash Man's special weapon. It stops time for a limited time and doesn't cause any damage, except when it is used on Quick Man; he is weak to this weapon and will lose one bar of his life for every two bars of energy Mega Man uses. It doesn't work on all the enemies; some enemies will only be slowed down by the Time Stopper and some are not affected by it at all.

Another serious downside is that, unlike Flash Man, Mega Man cannot shoot while this is active, nor switch to another weapon until the energy is finished (later in the series, Bright Man's Flash Stopper remedied this dilemma to some extent).

The Time Stopper's most famous use is to stop the deadly lasers on Quick Man's stage, allowing the player to bypass the laser area more easily.

The Doc Robot from Mega Man 3 also used this weapon along with the weapons from the other Robot Masters from Mega Man 2, but the player can't take it from Doc Robot.

Along with the Tornado Blow, Time Stopper is one of the few weapons that you don't have enough energy in one stock to eliminate the Robot Master that it's weak to.

Capacity
In Mega Man 2, Time Stopper can be activated only once, quickly draining the weapon's energy as time passes, and can't be stopped until all energy is drained. It only stops if Mega Man dies while it's active, leaving some energy to be used later.

Bosses weak and immune to Time Stopper
Quick Man is the only boss weak to this weapon. All other bosses from Mega Man 2, Mega Man: Dr. Wily's Revenge and Mega Man: The Wily Wars are immune to this weapon.