Decapitation

Decapitation is the act of cutting off a being's head. It can be used to disable certain supernatural beings, such as vampires, shapeshifters, arachnes, Leviathans and even demons.

Vampires
Chopping off a vampire's head will kill it.

Ghouls
Complete removal of the head is lethal for a ghoul.

Zombies
Zombies can be killed by decapitation as demonstrated in Dead Men Don't Wear Plaid when a few were killed through decapitation by shotgun blast. This also works on Croatoan zombies as demonstrated by Castiel in Two Minutes to Midnight.

Deities
Leshi could only be killed by being beheaded with an axe made of iron.

Arachnes
Beheading will kill an arachne.

Shapeshifters
Chopping off a shapeshifter's head will kill it, even their alpha.

Jefferson Starships
Cutting off a Jefferson Starship's head will kill it.

Leviathans
A Leviathan's head can be chopped off, which can be used to stop it temporarily, until it eventually reattaches itself. If the head is kept at a significant distance away from the body it will not reattach and the Leviathan will be immobilized forever until its head reattaches.

Demons
A demon's vessel's head can be chopped off, but, through possession, they can move it and sow it back on. If a demon is shot in the head with a devil's trap bullet and then decapitated it will remain immobilized forever unless the bullet is removed.

Nachzehrers
A nachzehrer's head can be chopped off but it will remain animated unless a copper coin is placed in the mouth first. If a copper coin is in the nachzehrer's mouth before they are decapitated, they will be killed. Otherwise, the head can be put back on the nachzehrer's body and reattach itself.

Bisaans
Bisaans can be killed by decapitation.

Humans
Being entirely mortal, humans can be killed through decapitation as well. Dean was able to kill Cuthbert Sinclair through decapitation with the First Blade.

Pontianak
Riza Nodd was killed by decapitation by Dean after Sam put Riza to sleep with a railroad spike through the back of her neck. It should be noted this is non-canon.

Werewolves
Mary Winchester was able to kill a werewolf in 1980 through decapitation with a shotgun.

Constructs
Gog and Magog could be killed through decapitation though only if it is done with a God-crafted weapon.

Appearances

 * Season 1
 * Nightmare
 * Dead Man's Blood


 * Season 2
 * Bloodlust


 * Season 3
 * Fresh Blood


 * Season 4
 * It's A Terrible Life
 * Jump the Shark


 * Season 5
 * Free To Be You and Me
 * Fallen Idols
 * Dead Men Don't Wear Plaid
 * Hammer of the Gods
 * Two Minutes to Midnight


 * Season 6
 * Live Free or Twihard
 * Family Matters
 * Caged Heat
 * Unforgiven
 * My Heart Will Go On
 * Mommy Dearest


 * Season 7
 * Shut Up, Dr. Phil
 * Slash Fiction
 * Out With The Old
 * There Will Be Blood
 * Survival of the Fittest


 * Season 8
 * We Need To Talk About Kevin
 * Blood Brother
 * A Little Slice of Kevin
 * Citizen Fang
 * As Time Goes By
 * Freaks and Geeks
 * Taxi Driver
 * Clip Show
 * Season 9
 * Devil May Care
 * Blade Runners
 * Alex Annie Alexis Ann
 * Bloodlines


 * Season 10
 * Ask Jeeves
 * Hibbing 911
 * The Werther Project
 * Brother's Keeper


 * Season 11
 * Baby
 * Don't You Forget About Me
 * The Chitters


 * Season 12
 * Keep Calm and Carry On
 * Celebrating The Life Of Asa Fox
 * First Blood
 * The Raid 


 * Season 13
 * Tombstone
 * The Scorpion and The Frog
 * Good Intentions 
 * ScoobyNatural
 * Bring 'em Back Alive


 * Supernatural: Fresh Meat 
 * Supernatural: Cold Fire