2spooky Windows game

Zombie
Speed: 3-4
Health: 4
Attack damage: just under 10%
ABILITY: They come in groups, usually outdoors in wide spaces. In the first level, you are weaponless and need to run from zombies.

Phantom
Speed: 1 (pretty slow)
Health: 1
Attack damage: 20% (big, but gives you enough time to defend yourself)
ABILITY: Invisible unless attacking. The only time you can see it is when it's right up in your face.
HOWEVER: You can take it down with one hit. It also makes a characteristic noise to give away its presence so that you're at least aware it's somewhere, coming towards you at the suspenseful speed of 1/10...

Bat
Speed: 8 (damn fast)
Health: 1
Attack damage: 5%
ABILITY: They come in large numbers, and they're really fast. You can't run from them.

Ghost in a keg
Speed: 0
Health: 2
Attack damage: 5%
ABILITY: Disguised as a keg, in a map full of kegs. It is positioned right beside a door, where the player would surely be within reach. When the player is attacked, they see nothing attacking. If the player happens to shoot the harmless-looking keg, the ghost is revealed for a split second as it demises.
ALTERNATE IDEA: The keg ghost follows the player very, very slowly, so that the player doesn't realize until it's in the way. In this case, the attack damage would be significantly larger, like 50%, so that the player would keep wondering what so instantly killed them.

Stalker (final boss)
Speed: 1
Health: Insane
Attack damage: 2.5%
ABILITY: Whilst you're busy entering in and out of rooms and corridors trying to find a key, the Stalker is following. You shouldn't bother trying to kill it either; it's too strong and you don't have enough ammunition. How could your night get any more frantic?