Number

 Number is a virus from Mega Man Battle Network 3. These can only be engaged on the field in event battles. It acts as a firewall to prevent the player from accessing certain areas.

No specific image is tied to a specific variant of the virus. Also, the virus is known to change its color as the battle progresses.

The virus must be destroyed in one hit in order for it to be destroyed. Otherwise, its HP returns to maximum. One can be destroyed at a time. If the viruses are not deleted in a specific amount of time, the viruses will unleash a devastating attack that can delete MegaMan.