Endings

Spoilers Ahead

Silent Hill 2 boasts six endings, none of which are confirmed to be canonical. The "In Water" ending is considered by most to be the "true" ending. Team Silent has made comments on it before, but have never confirmed which ending is the real ending. This gives players the freedom to decide which one they prefer or think is the best.
Two of the endings are "joke" endings, and require a bit more effort to unlock.

Leave

To unlock this ending, James must not be too self-destructive and must favor Mary over Maria. This can be achieved by healing quickly and keeping it in the green, listening to the entire conversation with Mary in the hallway leading to the final boss, examining Mary's photo and letter multiple times, and bumping into Maria and/or letting her take damage from monsters.
In this ending, James wants to continue living. We see him leave the town with Laura, leaving through the same graveyard he passes on the way in.

Maria

This ending is unlocked if James shows a lot of attention to Maria. By spending 10+ minutes near her, protecting her from monsters and not bumping into her, and not listening to the full conversation in the hallway or examining Mary's photo or letter. You also don't want to heal in excess, but do not keep your health low for too long.
In this ending, James walks back to the car with Maria. Almost there, she coughs. James tells her, "You better do something about that cough", implying that what happened to Mary will happen to Maria, and he will be the one to kill her, too.

In Water

James must act suicidal or reckless to get this ending, while also keeping a strong attachment to Mary. To get this ending, you must keep your health below 50% (in the red) for as long as possible. Examine the knife Angela gives you, read the suicidal diary entry on the hospital rooftop, and go to Neely's Bar after the hospital to read the new message left on the wall. ("There was a HOLE here. It's gone now." changes to "If you really want to see Mary, you should just die. But you might be heading to a different place than Mary, James.") You also need to listen to the full hallway conversation and allow Maria to take damage.
In this ending, we hear James get into his car and say that he can't live without Mary. We hear the car drive and crash into the water. We see sunbeams coming in through the surface of the water as Mary's final letter is read to us.

Rebirth

After completing the game once, four collectable ceremonial items can be found in New Game Plus. These items are the White Chrism, Book: "Lost Memories", Obsidian Goblet, and Book: "Crimson Ceremony". With the items in your inventory, after defeating the final boss, you will receive this ending regardless of your actions during gameplay.
We watch James rowing a boat on the lake with Mary's body. He talks about the Old Gods of the Lake, and believes they still remain, and can bring her back. This is a tie-in with the heavy cult themes of the first game.

Dog

To unlock our first joke ending, you must receive the three main endings (Leave, Maria, In Water) in the same save file, or have completed the Rebirth ending. In New Game Plus, find the Dog Key in a doghouse around the town earlier in the game. After watching the videotape in room 312 of the hotel, use the key to unlock the Observation Room in the third floor hallway.
James opens the door and finds a shiba inu with headphones on (Mira) pulling levers and watching tv screens. Speaking Japanese, he's in disbelief that this dog has been controlling everything. He collapses to his knees and hands, and Mira licks his face. We cut to the credits, which is shows a closeup of Mira's head on the right while funny clips and silly music plays.

UFO

Another joke ending, this only exists in the Greatest Hits or Director's Cut versions of the game. After completing the main game and the special Born From A Wish sub-game, the Blue Gem item can be found in the restroom at the very beginning of the main game. This gem must be used in three places throughout the game: in the Nightmare Hospital's Garden immediately after defeating Flesh Lips, on the Toluca Lake sock after defeating Eddie but before stepping into the boat, and near the back window in room 312 in the Lakeview Hotel before you watch the videotape.
Once the gem has been used in all three locations, the game immediately ends and is replaced with this ending. In the style of a silent film, a wave of UFOs decends the sky outside of the window. James meets up with Harry from the first game (still in the same PS1 graphics style). Harry asks if James has seen a little girl. James is confused and asks if Harry has seen his wife. An alien shoots James, and as the alien and Harry carry James back to the spaceship behind them, the camera zooms in and Harry gives the camera a thumbs up.