Guardin' Gnome is a Left 4 Dead 2 achievement for the Xbox 360 and PC. It involves winning Gnome Chompski from a shooting gallery on the second chapter of Dark Carnival and carrying him onto the rescue vehicle. Completing the achievment will earn Xbox 360 users Rochelle's shirt as an avatar award.
When initially trying to get Gnome Chompski, you must play a shooting gallery game and score 750 points. The game can be started by pressing the "activate" button while facing the button on the counter. Note that the button will not have an aura arount it, like weapons of health kits might. When playing, shoot targets for points. Shooting Moustachio will award you 100 points, while shooting Lil' Peanut will cause you to lose 100 points, so be careful. Shooting multiple targets with one shot will gain bonus points. The most effective weapon in the gallery would most likely be an AK-47, because of it slow rate of fire, allowing you to easily fire off the one shot needed to hit a target. If not available, an M-16 Assault Rifle will work well, too. If none of those are available, a Submachine gun, silenced of otherwise, will work. Throwing a Molotov in the gallery will work, as any targets that touch the flames will act as if they were hit. Be careful, however, as this may cause you to hit Lil' Peanut. It may be helpful to have full captions on during the game, as it will announce it noticeable pink words if Lil' Peanut or Moustachio are about to appear.
When 750 points have been scored, the red box to the left of the shooting gallery will open, allowing you to carry Gnome Chompski like a propane tank or gas can.
From then on, the gnome must be carried for the rest of the campaign. It has to be brought into the safe room to allow the gnome to be rescued. It can be dropped and picked up whenever the player chooses. When carried, the carrier cannot shoot, only shove with the gnome. It is not effective, taking 4 hits to kill a Common Infected, and roughly 7 to kill Smoker, Hunter, Boomer, Jockey, or Spitter. The carrier should be prepared to drop Chompski at a moment's notice to fight a Tank, horde, etc.
As a preemptive move to fight off death during a crscendo event, dropping Chompski in a safe location would be useful. Like, before you start the roller coaster crescendo, you may want to drop Chompski near the activating panel, then, when you have turned the alarm off, go back for him. Or, during the Barns, it would be beneficial to throw Chompski over the fence where the crescendo will take place, as it is more than likely you will want an extra gun to fight in it. You can throw him over the fence and grab him when the Infected are distracted by a pipe bomb or bile bomb.
When doing the finale, if holding out on the stage, it might be a good idea to put Chompski behing the sound board. This protects hhim from explosion, Boomer bursts, etc. It isn't advised to hold Chompski throughout the entire finale, only when you are racing to the rescue vehicle. Remember, Chompski must be held by a player, not just dropped in the helicopter, or else the achievement will not trigger. Note that any players that didn't touch the gnome or were dead or incapacitated outside the rescue vehicle will still recieve the achivement as long as at least one person with Chompski gets away.