Little girls like doll houses right? So it's set in a demented/twisted doll house filled with dolls that have twisted faces and red eyes. The starting room is the living room and stairs that lead to a small cramped hallway with pictures of zombies and such, since she controls them.
The zombies come from two windows on either side of the front door, A hole in the wall of the hallway, a hole under the stairs, and a hole near a Television.
The zombies would be dressed as a combination of American "Five" zombies, Nazi zombies, Soviet "Ascension" zombies, and 1940's era civilian zombies. A new special round zombie could be large bats about the wingspan of the characters shoulder width. They would circle you a few times then come in for a quick strike. Their poison would cause you to walk much slower. The map would turn a purplish tint with wisps of black smoke swirling away from wherever the bats fly (like a helicopters blades). They would make loud screeching noises and a [i]woosh[i] noise when they are near you. When they strike they make a loud deep bellowing sound. Lightning will flash more often than normal.
There will be a huge amount of rooms to explore, being that this is a mind game created by Samantha. The rooms themselves will be huge to tiny, to M.C Escher like.
New perk machines could include Mountain Spew: When you knife a zombie, they become a living grenade, exploding a few seconds after you knife them. they will explode after 10 seconds allowing you to get away, and zombies affected by it will have a green aura around them. It tastes like a lime to the characters (i'll let you decide which characters like it or not, also, can you think of some other perks? I'm kinda lost here.)
The new wonder weapon could be the der Suchende Pistole, or the seeker gun. The bullets would follow zombies until they hit it.
You could go into a graveyard in the back and some graves will spawn zombies. The pack-a-punch would be located in the basement, a door which could be opened after turning the power on. The power is on the roof, as an antennae that must be moved a little to the right to activate. But on the the roof lightning will be attracted towards you.
also a ghost of Samantha could be special enemies to fight and will steal all of your perks and the gun you are holding. Killing her without her stealing anything will bring the round counter back two levels (lowering the difficulty for a moment) and giving you a random pack-a-punched gun.