Energy absorption

Absorption was the ability to drain generally life force. However, others forces are also absorbed.

Witches

 * Willow Rosenberg demonstrate this ability when she becomes a evil witch by absorbing all magic force in Rack, since [Rupert Giles.

Demons

 * Der Kindestod drain life force only from feverish humans.
 * The Tak horn sported by Kungai demon had the ability to drain the life of those stabbed with it, leaving behind little more than blackened ashes.
 * The Root Monsters had the ability to drain life force from all living being and even others demons like Groosalugg.
 * The Smile Time cast had the faculty to absorb life energy from children.

Glorificus

 * Glorificus had the capacity to drain sanity from humans.

Others

 * The Inca Mummy absorb life force from his victims for restorate a temporary human appearence.
 * The babies Bezoar drain energy to future human hosts for preparate their coming.

Appearances

 * "Inca Mummy Girl"
 * "Bad Eggs"
 * "Killed by Death"
 * "Parting Gifts"
 * "No Place Like Home"
 * "Blood Ties"
 * "Tough Love"
 * "Couplet"
 * "Two to Go"
 * "Grave"
 * "Smile Time"