Zombie Apocalypse

For this trophy, you can get by yourself, but it would be a lot easier with 3 other people. If you're going to do this by yourself, you will need to be using the Chainsaw Execution (L1) on most or all of the zombies. That can increase your risk of dying and losing your multiplier, but it is possible. If your going to be using 3 other people, than have 2 people use the Chainsaw Execution and have the other 2 just killing them.

Optional way: Beat the game and unlock the '7 Days of Hell' mode, than stand in the corner and just shoot all the zombies, which will make the multiplier increase rapidly.