As someone once said, the Gnasher is the Bread and Butter of Gears of War. It is almost as iconic as the Lancer Mk2 and carrier remarkable power. Even at a decent distance, this weapon is capable of an instant kill with a single shot and at medium range, it is capable of downing enemies in as few as two shots. It is useful in the campaign mode for all sorts of situations but the weapon truly shines in competitive multiplayer.
When used in multiplayer, it is the go-to weapon in most situations. Most combat involves rapid movement in small spaces and even when there are large spaces, most of the combat revolves around getting up close on someone's flank to use this powerful weapon. Get familiar with it and the ranges at which it is effective because you'll get a lot of use out of it.
