Poltergeist

The  is a mutant of unknown origin which appears in the S.T.A.L.K.E.R.: Lost Alpha standalone mod.

"Supernatural in the eyes of some, invisible creatures haunting the deeper reaches of the Zone, usually haunting old, abandoned buildings. Nothing is known about their origin, although rumors in circulation claim they are spirits of stalkers hit by a massive wave of radiation. Their mysterious appearances and disappearances seem to correspond to the Poltergeist legend, hence the name. Known encounters with Poltergeists are quite diverse in fact: from mischievous laughter and blood-chilling howling, to deadly fireballs appearing out of nowhere. Unfortunately, all information about the Poltergeist phenomenon originates from unclear and contradictory stories of questionable validity."

- encyclopedia description

Overview
Supernatural in the eyes of some, invisible creatures haunting the deeper reaches of the Zone, usually haunting old, abandoned buildings. Nothing is known about their origin, although rumors in circulation claim they are spirits of stalkers hit by a massive wave of radiation. Their mysterious appearances and disappearances seem to correspond to the Poltergeist legend, hence the name. Known encounters with Poltergeists are quite diverse in fact: from mischievous laughter and blood-chilling howling, to deadly fireballs appearing out of nowhere. Unfortunately, all information about the Poltergeist phenomenon originates from unclear and contradictory stories of questionable validity.

Biology

 * Poltergeists are extremely deceiving for rookie stalkers, as they do not appear threatening; they only appear as a ball of electricity. However they can be killed with conventional weaponry just by shooting at the ball of lightning. Poltergeists will attack with anything that's not tied to the ground by utilizing their telekinetic powers to throw objects at the player (e.g., buckets, barrels, ammo boxes, crates, discarded firearms).

Gameplay

 * These are not strong mutants and, as mentioned above, may be dispatched with low-level weaponry. Note that due to their ethereal nature, the knife is not of practical use.
 * From v1.4000+ a group of eight now spawn in the Road Tunnel underground during the mission to rescue Nimble.
 * They are quite able to pass through closed doors.
 * Since the player has poor resistance to impacts and ruptures at this stage of the game, avoiding the various 'thrown objects' is desirable (bandages are not in plentiful supply in DC versions)
 * A Sawn-off Double-barrel Shotgun is very effective with only a shot or two needed per opponent.