Ghost

Ghosts, also called shades, wraiths, lemurs, haunts and specters   are spirits formed by the psychic footprints of people who are dead as opposed to lingering souls. Ghosts first appear in Grave Peril.

Description
Ghosts aren't alive, they are a "footprint in stone", they're "shaped like the original" human, but they aren't it. They are made up of memories.

The most dangerous ghosts are very substantial and appear to be human feeling real emotion. A shade with a greater sense of self or purpose can maintain its individuality and state of mind.

They do not play by the rules of reality, and they cannot be affected by someone whose presence they do not acknowledge. Most ghosts dwell at the very edges between the Nevernever and the mortal realm, though they can cross over to the mortal realm with relative ease at graveyards and sites of importance during their lives or during Halloween. Faith magic works best against these spirits. The Fae can also interact with them. Ghosts are drawn to the magically gifted. Ghosts may also be summoned by ectomancers in order to contact their loved ones, or to gather information.

A ghost's power may vary according to the strength of the deceased's psychic presence, varying from shades to very substantial ghosts, such as Agatha Hagglethorn or The Nightmare.

As already mentioned, not all ghosts are of equal power. Weaker shades may just have phantom-like forms, while others may be more defined and substantial. More powerful ghosts may interact with the mortal realm more actively than weaker ghosts. Agatha Hagglethorn was able to turn off the power in an entire ward at a hospital, enchanting the entire floor into a sleep, as well as using her spirit-self to suffocate babies.

They can also teleport or possess inanimate objects. The presence of a strong ghost can make the flame on a candle burn "pinpoint-clear".

Ghosts cannot roam the mortal world between sunrise and sunset, nor can they wander on holy ground. The only way a ghost can manifest is if it is insane.

Ghosts are also vulnerable to what Harry Dresden calls ghost dust, both in and out of the Nevernever. They can be trapped in a circle and then harmed by fire, or blocked by thresholds. When wounded, they bleed ectoplasm.

Ghosts can be sensed by priests, shamans, and people who care for the souls of others. They can also be sensed by dogs, about one in ten can, and cats, who are not very impressed by them.

Wraiths
Wraits are ghosts without a purpose or without sufficient memories and self-reason, devouring the memories and the life of other shades.

Harry Dresden describes them as humanoid grey forms floating above the ground. They have no real features, only hollow eye sockets in a skull-like face. Its mouth stretches open as though the lower jaw is hinged on rubberbands. Its details were obscure and oddly proportioned. It moves as though it has no weight and propelled itself by its toes.

Since they gave themselves up to despair, they have a cold presence and are very dangerous, especially to fresh shades, devouring their memories and assuming their power. With enough power, they can threaten mortals as well as spirits

Wraiths make a hollow rattling gasp as though out of breath to scream. When they expire, a stream of warped shadowy images play on a cloudy vapor that is emitted from their forms like series of old random movie clips.

In Ghost Story, a wraith nearly consumes Harry Dresden's ghost but Sir Stuart kills it with a memory bullet. Wraiths were brought as attack-dogs by lemurs to charge Mortimer Lindquist's house—the Grey Ghost was apparently behind the ghostly attack.

Later, the Grey Ghost, reveals to be Corpsetaker, tortures Mortimer Lindquist by lowering him into a pit of wraiths. The following night Harry Dresden comes to his rescue, accompanied by with his army of ghost soldiers and specters. After Harry released Morty, he sends all of the Wraiths against the Corpsetaker getting her off of Molly Carpenter, and pushing her into a Southbound Train from Between.

Lemurs
Lemurs are ghosts that gave themselves over to rage and malice. They are dressed in dark robes and know no pity or restraint. Harry Dresden describes them as dark, slithering shapes. They look vaguely like they were cloaked in dark robes. They move amongst the wraiths with them like sharks after blood.

In Ghost Story, they attack Mortimer Lindquist's house bringing wraiths with them as their attack dogs.

A group of three lemurs attack Harry Dresden's ghost taking chunks out of him and consuming them until Waldo Butters and Bob came along. Butters gave permission for Bob to leave his skull and save Dresden from the lemurs. He destroyed them leaving floating, glittering, multicolored gemstone shapes. To repair Dresden, Bob's spirit gathered all the gems and made him eat them; Dresden feels better instantly.

The Corpsetaker again tortures Mortimer Lindquist while the lemurs sat in an outward facing circle toward the main entrance not the Nevernever. The Lecters destroy about half of them.

Specters
Specters are semi-corporeal ghosts.

Corpsetaker calls up a number of Specters to attack Grevane's zombies outside Harry Dresden's apartment. According to Mab, "Specters most potent" that are "beyond the beck of the mortal pale, will rise up to the night and the stars at the sound of his horn, and join the Hunt.", Harry translates: "So, a gaggle of wizards who stock-in-trade is enslaving the dead to their will is interested in a being (Erlking) whose presence calls up powerful spirits they couldn't otherwise reach."

Near the site where the Darkhallow is being performed, hundreds of specters rose up out of the ground where Harry, Butters, and the Wardens were. Butters empowers a circle and kept up a steady beat for Sue. Kowalski was killed by specters when they rose up out of the floor underneath him, he didn't have a chance. In Ghost Story, the insane serial-killer ghosts can manifest and were dubbed: "Lecter Specters".

Groups
There are groups of ghosts that more or less act together for their own reasons.

Sir Stuart's Ghost-Soldiers
They are guardian spirits or protecter spirits  of Morty's house and are more than spirit soldiers. They were "ghosts of duty and obligation unfulfilled, had remained behind to see their task to completions." They were shades of faith, love and duty. The served as a balancing energy with the dark power for the killer ghosts.

They were wispier and foggier, less defined and were the size of a mob. The ghost army soldiers ware all from Different eras: Revolutionary War, buckskin woodsmen, trappers, Native Americans from wars proceeding that one, farmers from the Civil War, shopkeepers from the turn of the century, men in suits, some with shotguns or tommy guns, doughboys from WWI, Buffalo Soldiers, gun-toting cowboys, and Vietnam War grunts.

They aid Lindquist out of friendship and respect rather than compulsion. They had become faded over time from loss of too many memories, forgetting their mortal lives little by lithe. They are sane, so they can not manifest, nor they could stop Boz from killing Lindquist.

The Lecter Specters
All the ghosts watching Mortimer Lindquist’s house as it burned were killers, Mort gave them a home, a reason to turn aside their madness. With Mortimer gone, they will kill again. According to Sir Stuart, ”fifty years of maddened shades unleashed upon the city all at once. Preying on mortals. Blood will run in buckets.”  Harry told Murphy that if they don't get Mortimer back, that they manifest making them real like the Nightmare.

Harry dubs them the insane killer ghosts the Lecter Specters. Since they are insane, they can manifest—sane ghosts don't interact with the mortal world. There were some famous Chicago serial killers amongst them.

The Lecters answered Harry's call to come home at Mortimer Lindquist, along with the Ghost-soldiers, and follow him to rescue Mortimer. They fought Evil Bob's forces in the Nevernever and fought the lemurs and Big Hoods in the hideout. Corpsetaker ate them, like the Darkhallow. She did that to gain enough madness to manifest and some of her powers back with the ability to steal any body.

Wolfwaffen
The Wolfwaffen were a part of the Evil Bob's defenses of Corpsetaker's stronghold from the Nevernever side. They wore the bland-and-gray uniforms of the old Waffen-SS. Their faces were distorted into the jaws and muzzle of a wolf but bearing no fur. Their eyes were black empty holes—there were no eyes, just sockets. There were machine-gun crews, rifle men—"riflethings". They looked hungry to spill blood, or rather ectoplasm.

Grave Peril
In Grave Peril, something was stirring up the ghosts in Chicago, including Agatha Hagglethorn and the Nightmare.

Dead Beat
In Dead Beat, Corpsetaker uses Specters as soldiers.

Ghost Story
In Ghost Story, Lemurs repeatedly attack Mortimer Lindquist's house using wraiths as attack dogs and led by the Grey Ghost and Evil Bob.

Father Forthill sensed the chill of Harry's Ghost when he neared him. Sir Stuart said that he must be one of the "good ones": minister, priest, shamans, whatever. Spending your life caring for souls tends to give them the ability to sense spirits, though not exactly soul, ghost aren't that much different.