This achievement requires you to kill 53,594 Zombies. Luckily, unlike the original, your TOTAL NUMBER OF KILLS FROM EVERY PLAYTHROUGH goes towards this achievement, so if you do not want to drive around underground for hours and hours, you can just play the game and eventually unlock it. If you're trying Seven Day Survivor, then you should try to do this first to get the Real Mega Buster. I made another guide about all of the changes to Infinity Mode as well.

- First thing to know, this achievement takes a lot of time. You're best starting a new game and skipping every mission right after making it into the Security Room.

- The best way to rack up a lot of zombie kills is once again driving a vehicle in the Maintenance Tunnels.

- Once you get to the Security Room and get the Backup for Brad mission, ignore it completely and head for the Tunnels through Leisure Park.

- Take the Red Sports Car into the tunnel (there is now a barrier you need to press in order to zone into the tunnels now, do not smash your car on it).

- Take a left towards the Meat Processing Area, avoiding any zombies pushing gas tanks.

- Once you arrive at the Meat Processing Area, take the Truck.

- This time, instead of taking the truck all the way down to the other side of the tunnels, simply go halfway down the road until the zombie cluster respawns by the processing plant. If you do your best to avoid the gas tank zombies on the road and hit every zombie in the cluster, it should be around 200 zombies every time.

- The truck has better endurance this time, so now it can hit anywhere from 1,500 to 1,700 zombies before it breaks.

- Once it breaks, zone into the Meat Processing Area, grab some milk, and go back to the truck and repeat this until you get 53,594 kills.

- Once you finish the route and get the achievement, head back to the Security Room.

- Save your progress to be safe and then speed up time till the Helicopter arrives and be at the Helipad at 12 PM as you MUST GET AN ENDING.

- Yep, that's it. This achievement is known for being incredibly long and boring, but it is worth it for the Real Mega Buster.

- In this game, you can hold the shoot button to charge up a huge explosion from the Mega Buster. It's cool.