The Gage Ninja Pack Add-on for PAYDAY 2 has 4 achievements.
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.
Have at least 3 enemies poisoned at the same time with your poisoned weapons. Unlocks the "Shirai" mask, "Origami" material and "Hanabi" pattern.
Get eleven kills with the Lebensauger .308 Sniper Rifle without reloading it. Unlocks the "Slicer" mask, "Still Waters" material and "Youkai" 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.