This is a guide to show you how to get the endings in all of the games.
Silent Hill
Good+ Ending
Save Cybil and complete the Kaufmann sidequest
Good Ending
Kill Cybil and complete the Kaufmann sidequest
Bad Ending
Kill Cybil and don't complete the Kaufmann sidequest
Bad+ Ending
Save Cybil and don't complete the Kaufmann sidequest
UFO Ending
Use the Channeling Stone on top of the lighthouse
Silent Hill 2
????
Silent Hill 3
????
Silent Hill 4: The Room
????
Silent Hill: Ørigins
Bad Ending (unlocks Butcher costume and Great Cleaver)
Kill 200 enemies on subsequent playthroughs
Silent Hill Homecoming
Good Ending (unlocks Big Rig costume)
Kill Lillian, forgive Adam
Drowning Ending (unlocks Order Soldier costume)
Kill Lillian, don't forgive Adam
Judgment Ending (unlocks Bogeyman costume)
Don't kill Lillian, don't forgive Adam, don't save Wheeler
Hospital Ending (unlocks ER costume)
Don't kill Lillian, forgive Adam
UFO Ending (unlocks Deputy costume and Laser Pistol)
Don't kill Lillian, don't forgive Adam, save Wheeler
Silent Hill: Shattered Memories
????
Silent Hill
Good+ Ending
Save Cybil and complete the Kaufmann sidequest
Good Ending
Kill Cybil and complete the Kaufmann sidequest
Bad Ending
Kill Cybil and don't complete the Kaufmann sidequest
Bad+ Ending
Save Cybil and don't complete the Kaufmann sidequest
UFO Ending
Use the Channeling Stone on top of the lighthouse
Silent Hill 2
????
Silent Hill 3
????
Silent Hill 4: The Room
????
Silent Hill: Ørigins
Bad Ending (unlocks Butcher costume and Great Cleaver)
Kill 200 enemies on subsequent playthroughs
Silent Hill Homecoming
Good Ending (unlocks Big Rig costume)
Kill Lillian, forgive Adam
Drowning Ending (unlocks Order Soldier costume)
Kill Lillian, don't forgive Adam
Judgment Ending (unlocks Bogeyman costume)
Don't kill Lillian, don't forgive Adam, don't save Wheeler
Hospital Ending (unlocks ER costume)
Don't kill Lillian, forgive Adam
UFO Ending (unlocks Deputy costume and Laser Pistol)
Don't kill Lillian, don't forgive Adam, save Wheeler
Silent Hill: Shattered Memories
????