Undead Overrun is a multiplayer mode in which hordes of zombies will keep attacking the player until the player dies, with a maximum party of 4. Each wave has a time limit which may be extended by opening a coffin, which will also give ammo. Any player can heal another player if he/she is down.
Here are some tips:
- Keep Moving: Don't seek cover.
- Aim for the Heads: Ammo is rare, and headshots are an instant kill.
- Team-Up: If you split up it will only get harder, stay close, save your ammo and try to execute if possible.
- Play with 4 players: Obviously makes it easier, doing it with 2 is hard, 3 is doable and 4 is rather easy.
- You only have to complete Wave 14, if you die or the time runs out there, the achievement will still unlock.