Round 1.- Knife the zombies while they attempt to enter

Round 2.- you are still upstairs, 5 shot each zombie then knife, try to do it before they enter because it will be harder

Round 3-8.- open downstairs, grab the thompson that is in front of the mistery box aside of a doorway, now go to the doctor's quarters door but DON'T open it, stay where the gate is with a table in front of it. You now have two perfect views of zombies.
When the dogs come between these rounds, go to the storage gate but dont open it, you have the thompson, stay there and now its easier to kill the dogs. Another way is run back and forward between two rooms and kill them while walking shooting from the hip.
In round 8 watch out not to kill the last zombie, instead cook a grenade and throw it to him, after he starts crawling seek for either the juggernaut or the sleight of hand in any island except com room because that is the hard lvls spot. after you searched for the juggernaut and where lucky enough to find it. Also if you get the wunderwaffe please try to change it for a better secondary weapon as MG but not the BAR.

Round 9+ .- Now here goes what you will do until you get the achievement you will be doing this, follow this video, but instead of doing it with the ray gun, try it with the PPSh and you can get also the headshots achievement.