Of the thirty Denarian coins, Father Forthill only possesses nine at the beginning of Death Masks. (The coin Sanya once held (that of Magog) is NOT among them, as we learn in Small Favor.) By the end of Death Masks, Ursiel became the tenth, then Saluriel the eleventh. Sadly, the Church of Rome displays no great ability to keep possession of the coins (in Skin Game Harry suggests sarcastically that whoever is in charge of them uses them to buy snacks from vending machines) and they seem to re-enter circulation quite easily.
Ursiel — the Denarian Sanya and Shiro dispatch in the beginning of Death Masks. His host was named Rasmussen, and he was taken over in 1849 on his way to California. Harry describes Ursiel first as looking like "a freaking grizzly bear" until he sees the details:
It wasn't a bear. Not unless a bear can have six legs and a pair of curling ram's horns wrapping around the sides of its head. Not unless bears can somehow get an extra pair of eyes, right over the first set, one pair glowing with faint orange light and one with green. Not unless bears have started getting luminous tattoos of swirling runes on their foreheads and started sprouting twin rows of serrated, slime-coated teeth.
Saluriel — Its former host was Quintus Cassius. Harry describes the transformation of Cassius into Saluriel this way:
[He] changed. A sheath of green scales appeared over his skin, and his legs twined together into a serpent's long and sinuous body. The eyes went last, changing to vertically slit yellow orbs while a second set of glowing green eyes opened above the first.
The nineteen remaining are:
"Anduriel. He was a captain of Lucifer's, after the Fall. Anduriel leads the thirty Fallen who inhabit the coins. Nicodemus wasn't seduced into Anduriel's domination. It's a partnership. Nicodemus works with Fallen as a near-equal and of his free will."
According to Kringle (as per Skin Game) Anduriel can potentially tap into the shadow of any mortal and use it as a surveillance device - unlike many of the Denarians, it specialises in intelligence work rather than combat.
2) Akariel — cut to ribbons by Thomas Raith's saber in Small Favor. Harry says of it, "I didn’t get a good look at it, but got an impression of spiraling antlers and green scales." Its former host is dead, his name unknown.
3) Imariel — Also called Mantis Girl, Harry's nickname for the Fallen hosted by Tessa, Nicodemus's lover. Second-eldest of the Denarians; only Nicodemus and Anduriel have been together longer. According to Harry, the Denarian has a voice "like out-of-tune violin strings stroked by a rotting cobra hide." Can reconstitute itself after being blown to smithereens by an assault rifle, and when Tessa is shot, "bursts of fluttering insect forms [fly] up from the gunshots instead of sprays of blood." Harry describes the demonic form of the Denarian this way:
…a creature barely more than the size of a child. It was red and black, vaguely
humanoid in shape, but covered in an insect’s chitin. Its eyes were too large for its head,
multifaceted, and its arms ended in the serrated clamps of a preying mantis. Membranous
wings fluttered at its back, a low and maddening buzzing.
And that wasn’t the scary part.
Its eyes gleamed with an inner fire, an orange-red glow—and immediately above the first
set of eyes another set, this one blazing with sickly green luminescence, blinked and
focused independently of the first pair. A sigil of angelic script burned against the chitin of
the insect-thing’s forehead.
In addition to the demonic abilities that she possesses courtesy of her partnership with Imariel, Tessa is a sorceress, and a very powerful one.
4) Lasciel — Harry's personal albatross.
The Seducer," Forthill murmured. He smeared his finger over the chocolate, erasing the sigil. "Lasciel is also called the Webweaver and the Temptress," he said, between licks. "Though it seems odd that Nicodemus would want to free her. Typically, she does not follow Anduriel's lead."
"A rebel angel among rebel angels?"
"Perhaps," Forthill said.
5) Magog — Its former host was Sanya, who is now a Knight of the Cross. Its host following Sanya is now dead, his name unknown. Harry describes Magog as having "a deep-chested bellow," "checking in at seven or eight hundred pounds" and as looking "like nothing so much as a big, leathery gorilla, except for the goat’s horns and heavy claws."
6) McKullen — Known only by the name of its now-dead host. May resemble a lizard-like thing.
7) Ordiel — Description and host unknown. Killed by Kincaid at the Oceanarium in Small Favor.
8) "Shaggy Feathers" — Harry's nickname for this particular Fallen. He describes it thus: "A second shapeshifted creature, this one covered in a shaggy coat of grey, dusty-looking feathers, its face a grey mass of fleshy, hanging tendrils, had my wrists pinned to the ground." Its former host is dead; its name unknown.
9) Tarsiel — May resemble, in Harry's words, "an androgynous, naked, bald statue of obsidian, green eyes glowing above human eyes of bright blue." Its former host is dead; his or her name is unknown.
10) Thorned Namshiel — Another powerful sorcerer whose unnamed host seemed to resemble a normal human with a number of bone spurs protruding through his skin. Seems to have been responsible for the hellfire based containment barriers used in Small Favour - notably at the battle of the Shedd Aquarium. He is also suspected of being responsible for the hellfire attack on Arctis Tor immediately before Harry's arrival in Proven Guilty. His host was killed during the First Battle of Demonreach but the resultant coin, briefly retrieved by Harry, then went missing. It may - or may not - be in the possession of Monoc Security.
Rosanna proved to be a rather beautiful-looking woman, the classical demoness with scarlet skin and a goat’s legs, complete with leathery black wings and delicately curling horns—though her deep brown eyes were haunted beneath the demonic green glowing set.
12) Unnamed Denarian — the first of two whose hosts were killed by Michael and Sanya at the Oceanarium in Small Favor.
13) Unnamed Denarian — the second of two whose hosts were killed Michael and Sanya at the Oceanarium in Small Favor.
14) Unnamed Denarian — the first of two whose hosts were killed by Captain Anastasia Luccio at the Oceanarium in Small Favor.
15) Unnamed Denarian — the second of two whose hosts were killed by Captain Anastasia Luccio at the Oceanarium in Small Favor.
16) Unnamed Medusa Denarian — Its host is Nicodemus' daughter, Deirdre. Harry describes her this way:
I recognized this one, which looked like a woman, except for the reverse-jointed legs ending in panther claws, the bright red skin, and the mass of metallic, ten-foot-long, independently moving blades in place of hair. Deirdre, Nicodemus’s darling daughter.
By the end of Skin Game this Denarian is now without a host, it's coin back in the possession of Nicodemus.
17) Unnamed Tree Root Denarian — In Small Favor, its host is a woman whose name we do not yet know. Harry describes her this way:
…a wizened little thing that looked like a caricature of a woman carved from a dried tree root seemed to be holding the end of a rope of liquid shadow that curled like a hungry serpent[.]
18) Urumviel — Description and host unknown. Killed by Kincaid at the Oceanarium in Small Favor.
19) Varthiel — Description and host unknown. Killed by Kincaid at the Oceanarium in Small Favor.
Unfortunately, all of the coins captured after the Oceanarium battle were lost during the first battle of Demonreach and although the Denarian suspected of stealing them1 was killed, the coins were not recovered and should be expected to be in the possession of his patron Tessa.
History of the Denarians
(Modified from the Dresden Files Wikipedia entry)
The Knights of the Blackened Denarius, also called the Denarians, are unions of a human host and a Fallen angel. There are thirty Fallen, each bound to a tarnished silver Roman denarius which bears its respective Fallen's sigil; the thirty denarii represent the thirty pieces of silver paid to Judas Iscariot, and are implied to be those very coins.
Once a human has physically touched one of the Blackened Denarii, the Fallen bound to it is free to communicate with its new host, able to bestow knowledge, physical prowess, and magical ability, for as long as the host maintains possession of the coin. Even if the human does not play host to the Fallen and tries through some means of binding the coin (through magic) the Fallen still leaves a sort of impression on the host that keeps a constant connection. Even this mental copy is capable of extreme power, such as casting life-like illusions.
The amount of influence a Fallen can exert over its host appears to vary—in the case of Ursiel, the Fallen had completely taken over the host body, and kept the host's soul tortured and trapped. In the case of Nicodemus and his Fallen Anduriel, the two work in a mutually beneficial partnership. In all cases, however, the free consent of the bearer is necessary to permit Fallen influence. If the Fallen has not completely overtaken its host, it appears that the host is able to consciously free himself or herself from the influence of the Fallen, simply by abdicating the power it provides and surrendering the Denarius. In the case of Quintus Cassius, a Denarian bonded with Saluriel, Cassius surrendered the coin to Knights of the Cross to avoid execution. Sanya admits to having once been a member of the Order, but he surrendered his Denarius freely prior to becoming a Knight of the Cross.
The Knights of the Cross were founded specifically to save people from the Fallen, and will almost always become involved (often by seeming random chance) in any situation that requires confronting one or more of the Denarians.
If the host of the Fallen is a wizard or magic-user of some sort, as most of those shown have been (although it is not clear if it happened before or after they became hosts), one way to be free of the Fallen is for the host to put aside magic forever and give up the coin.
Interestingly, on several occasions Nicodemus claims that the Denarians have a specific mission and, from their perspective at least, are trying to save the world as much as the "Good Guys" are. Of course, Nick could be lying - his faction do have something of a reputation for that - or the Fallen could, from their perspective, be trying to save the world from its Creator. Alternatively, they also might be struggling against Nemesis from a different angle.
Harry accidentally absorbs Lasciel's shadow at the end of Death Masks and instantly takes all precautions to keep her influence at bay. He keeps her secret to all but Bob and buries her coin in the concrete of his sub-basement floor with a series of magical barriers. However, Lasciel's imprint upon his brain cannot be undone.
She does not appear to Harry until Dead Beat. Wanting to gain Harry's trust, she manifests herself as a young woman named Shiela, whom Harry "meets" at Bock's bookstore. Shiela helps Harry on several occasions, once using her photographic memory to recall a spell to summon the Erlking, which would throw a wrench in the evil necromancers' plans. She also serves briefly as a potential romantic interest for Harry, but this ends when Harry realizes Shiela is an illusion.
Over the following books, Harry walks a thin line with Lasciel. He is reluctantly willing to use her gifts - Hellfire, her photographic memory, and her millenia of knowledge and experience, to name a few - though he is more than aware of the high cost he will eventually have to pay as a result. Harry finally comes clean about her to Michael in the end of Proven Guilty, and he is stunned to learn that Michael had known all along, having witnessed Harry accidentally acquiring the coin while protecting Michael's youngest son. Michael emphasizes his trust in Harry, but warns him that if he begins to fall, he and Sanya will take action.
In White Night, Harry begins to work on Lasciel, trying to convince her that she is independent of the Fallen Angel Lasciel imprisoned in the coin. He dubs shadow-Lasciel "Lash" as a means of differentiating the two. In the end, Lash is able to save Harry from an explosion at the Raith estate, but the result is mild brain damage for Harry. She chooses to restrict the damage to the portion of the brain she occupies, essentially destroying herself to spare Harry any injury. Even her sigil disappears from Harry's hand. Harry digs up her coin and leaves it in Father Forthill's care.
At a book signing shortly after the release of White Night, however, Jim teased audiences that we had not heard the last from Lasciel, and possibly Lash as well.
This would be demonstrated in Skin Game when the Coin reappeared in the possession (ahem) of Hannah Ascher. By the end of that case, the coin appears to have been left behind in Hades' vault and is thus likely to be out of circulation for some time.