You can unlock it in Training Camp (Tutorial)
Single target, medium range troop with moderate hitpoints.
You can backup higher higher hitpoint troos like a Giant.
Can target air and ground troops. She is a powerful substitute to Archers.
The Musketeer can attack from a distance without engaging the defending troops.
Well placed high level Minion Horde can destroy it quickly.
Use the Muskeeter to counter Baby Dragon.