I just beat it the reason the mission keeps failing is because it's 3 sets of zombies I never notice the 3rd set that's why the mission says failed when you shot a couple zombies I used 1 adrenaline to kill the first set all the way down at the bottom of the screen once you kill them the other 2 sets of zombies just waits on you to kill them they don't run or nothing and the board is actually easy once you kill the bottom set of zombies I hope this is helpful