Here is the full list of all 20 AT SUNDOWN: Shots in the Dark achievements.
Play your first match.
Play a game type other than Deathmatch, Timed, or Timed Deathmatch.
Play a match where you use 5 different weapons.
Complete a Training Challenge.
Get Gold in all Training Challenges.
Unlock everything.
Kill someone on a killing spree.
Kill someone on a killing spree and get a killing spree yourself.
Win a game where no other players get a kill.
Win a game with a triple kill at the end.
Get 10 kills on all weapons, including unlockable ones.
Get 1000 kills.
Win 100 games.
Win 500 games.
Play with a friend online.
Play an Unranked online match.
Play a Ranked match.
Play 3 Ranked matches in a row.
Win an Online match (Ranked or Unranked).
Win 10 Ranked matches.