The Gage Ninja Pack Add-on for PAYDAY 2 has 4 achievements.
Get eleven kills with the Lebensauger .308 Sniper Rifle without reloading it. Unlocks the "Slicer" mask, "Still Waters" material and "Youkai" pattern.
Have at least 3 enemies poisoned at the same time with your poisoned weapons. Unlocks the "Shirai" mask, "Origami" material and "Hanabi" pattern.
Kill 100 enemies in a single day of a heist with the Kross Vertex Submachine Gun. Unlocks the "Kage" mask, "Sakura" material and "Oni" pattern.
Complete a single day of a heist in stealth using only the Shuriken throwable and killing at least 4 enemies. Unlocks the "Kuro Zukin" mask, "Bamboo" material and "Koi" pattern.