The term apparition refers to ghosts or spirits of the dead who have returned to the world of the living. There are two types of apparitions – aggressive and peaceful.
Aggressive apparitions are violent spirits and will attack any living creatures they see. They can usually be found in places where the dead are uneasy, such as graveyards, or near old Hammerite temples. The most common ones represent the spirits of dead Hammerite Priests. They appear because of some wrong that was committed to them whilst they were alive, a desire to protect a place or object, or just sheer jealousy of the living. If the person was a magic user in his life, he will become a very dangerous ghostly entity. They can be recognized by their dreadful ghost speech, resembling words being said in reverse (the words are actually Viktoria's lines in the reveal scene in The Dark Project). Aggressive apparitions are truly a chilling entity and regretfully not that rare.
Hammer Priest apparitions are the most powerful enemies in the first two Thief games, and thus are difficult to bring down. Their main weakness is they don't hear anything. The best method of attack is a backstab followed immediately by a second hit. The second hit is required because they are so tough that a backstab alone cannot bring them down. When engaging one in battle, remember that it will take a lot of hits until it goes down. An Apparition can fire up to 3 simultaneous ghost skulls, and if Garrett is hit by more than one he'll be seriously injured. These projectiles can be dodged, however, if Garrett moves fast enough, and apparitions don't have any other form of attack. The key to victory is patience. However, there are few places where there might be more than one apparitions close to each other, and this can lead to serious trouble. The key in this situation is knowing when to run away. Some key points to remember when fighting apparitions:
- Backstab – The backstab is effective if unaware, but can cause a large amount of noise. DO NOT use if there are hostiles nearby. Take caution that one backstab may not be enough.
- Sword - Use only when the backstab failed. One or two hits should take care of it.
- Blackjack - The undead cannot be knocked-out.
- Broadhead Arrow - It takes 32 broadheads to kill, not recommended.
- Fire Arrow – It takes at least 3 arrows, but still effective. VERY LOUD! Use in groups of undead.
- Flash Bomb – 3-5, depending an alertness. Use in groups of undead.
- Holy Water Arrow – About 6 arrows, use in groups of undead.
The Ghost skull is a ranged spell cast by most Apparitions. The "projectile" consists of one to three spinning skulls. The skulls fly somewhat faster than a Hammerite Priest spell. On contact, these will explode into clouds of dust, injuring Garrett and any other living creatures in the line of fire. They can become a serious threat, especially in confined areas or when paired with other undead foes. Ghost skulls don't harm the undead.
Peaceful apparitions, as their name implies, are benign and will not attack Garrett. They are often referred to as ghosts. They usually appear in order to resolve unfinished business in their past life, or because of an emotional attachment to the area. They usually speak about their misfortune, but sometimes they give useful information. Other than that they represent no threat.
A sole exception to this is a hostile apparition in the mission "Casing the Joint" (and in "Masks" should it not be dealt with in Casing the Joint), which walks the halls of the Library, and will fire skulls at Garrett should it detect him. This specimen is immune to normal attacks, and is usually dealt with by reading a number of documents in the library, exorcising it. However, it is interesting that a Frogbeast Egg can still potentially damage it in some game versions, and will allow the apparition to be killed.
Peaceful apparitions do not loath the living, but rather enjoy their company, and ask the passersby for help in order to pass into the afterlife. If helped, the apparition returns the favor to Garrett by helping him solve a problem of his own. A notable example of an occurrence was when Garrett encountered Brother Murus in Return to the Haunted Cathedral. Garrett helped Brother Murus recover his things and in return, Murus helped Garrett escape the Cathedral.