Pyramid Head

Appearance: He shows up in the stairwell when you're leaving the Apartments. He will stalk you and Maria throughout the game though, and there will be a final confrontation at the end of the game.

Strategies: Never let him close you in! Always give yourself as much room as possible and shoot from a distance.

Flesh Lips

Appearance: When Laura locks you in the room at the Hospital, 3 or 4 of these will drop down.

Strategies: Keep a safe distance and shoot them until their feet crawl up.

Abstract Daddy

Appearance: Towards the end of the Labyrinth you'll run into him.

Strategies: Basically the same idea of keeping a safe distance and shooting this boss is the best way to go.

Eddie

Appearance: Right before getting to Lakeside Hotel you'll run into him in the meatlocker room.

Strategies: Some people have mentioned going into this fight with a melee weapon like the pipe, but I've always found that I could beat him with a gun. Just make sure to dodge his shots (they hurt a lot) by hidiing behind the hanging meat. It's most likely that you'll get hit once or twice, but he will be down by then.

Mary

Appearance: At the end of the game - Final Boss.

Strategies: She will try to strangle and stab you along with sending droves of moths after you. The best way to beat her is to keep moving to avoid her attacks and when their is a moment of safety - shoot her with your rifle.