Here is the full list of all 26 ASSASSINATION BOX achievements.
GET PROFILE LEVEL 100
GET "S" RANK ON EVERY LEVEL IN TAKEOVER MODE
GET PROFILE LEVEL 75
GET PROFILE LEVEL 50
FULLY UPGRADE MOVEMENT
FULLY UPGRADE SLOW TIME
GET "S" RANK ON EVERY LEVEL IN SURVIVAL MODE
FULLY UPGRADE ACTION POINTS
FULLY UPGRADE JUMP
FULLY UPGRADE GRENADES
FULLY UPGRADE DODGE
FULLY UPGRADE DASH
GET PROFILE LEVEL 25
FULLY UPGRADE AMMO
GET 100,000 ASSASSINATION POINTS
GET PROFILE LEVEL 10
FULLY UPGRADE MONEY
GET RANK "S" FOR THE FIRST TIME
FULLY UPGRADE HEALTH
BUY EVERY UPGRADE FOR ONE WEAPON
GET 10,000 ASSASSINATION POINTS
GET 100 HEADSHOTS
GET TOTAL 1000 KILLS
KILL 100 ENEMIES IN ONE GAME
BUY ANY CUSTOM PART
SO YOU ACTUALLY MANAGED TO RUN THE GAME