Is there just a single ending or are there different endings in Silent Hill: Downpour?
The game has 6 possible endings, but only 5 are available on the first playthrough. The ending obtained depends on 3 factors.
After the game's completion a new sidequest is added, Digging Up the Past, and completing this sidequest it rewards the player with the Surprise ending. Akin to Silent Hill 4: The Room, Downpour does not have a UFO Ending.
Ending A - Forgiveness: You'll obtain this ending by having good karma (choose to help when given the option) and sparing the character at the end.
Ending B - Truth and Justice: You'll receive this ending if you killed too many enemies, even if you had good karma otherwise by choosing to help the two other characters early on.
Ending C - Full Circle: Achieve this ending by having good karma (choose to help when given the option) but killing the character at the end.
Ending D - Execution: This ending is achieved by having bad karma (do not choose to help when given the option) and by killing the character at the end.
Ending E - Surprise: This ending is achieved by completing the Digging Up the Past side quest on your second play through.
Ending F - Reversal: Achieve this ending by dying at the end. Anna will wake up from a dream and be inside a cell, and Murphy will be a prison guard.
The video including all ending cutscenes: