Here is the full list of all 19 PEP achievements.
Kill 1 Player
Kill 10 Players
Kill 25 Players
Kill 50 Players
Kill 100 Players
Kill 10 Zombies
Kill 1000 Zombies
Kill 2000 Zombies
Kill 3000 Zombies
Kill 4000 Zombies
Kill 5000 Zombies
Fire 500 Shots
Fire 5000 Shots
Fire 50,000 Shots
Fire 500,000 Shots
Kill 10,000 Zombies
Kill 50,000 Zombies
Kill 100,000 Zombies