Shadow

"See, once a familiar becomes a warlock, they have until the next new moon to purge itself of its new life. If it succeeds, it becomes immortal. If it fails, it returns to its animal state for eternity. Shadow was a cat. So it has to shed all nine of its familiar lives."

—Ariel explaining Shadows' intentions.^[src]

Shadow was a former feline familiar who betrayed Ariel to become a warlock in the process. He then attacked the Charmed Ones, as he needed to shed his nine lives to become immortal.

History

Chance at Immortality

In 2001, Ariel was performing a ritual when her familiar, a cat named Shadow, jumped onto her lap and interrupted her. He then jumped up onto a table where many potion bottles were located and one by one knocked them onto the floor. The spilled potions killed Ariel and transferred her powers directly to him. This act of betrayal turned Shadow into a familiar warlock.

Attack on the Charmed Ones

Shadow knew that since he was previously a witch's familiar, specifically a cat, that he would have to shed all nine of his familiar lives prior to the next new moon to become immortal. He set out in search of the Charmed Ones in hopes that they would be strong enough to kill him all nine times. He first attacked the sisters individually and then set out to find them together.

The Charmed Ones, however, realized that Shadow was entirely too easy to kill, and summoned Ariel's spirit for help. Ariel told them what Shadow was really trying to achieve and told them not to vanquish him, as he would revert to a cat if he failed. Shadow realized the sisters were on to him, and instead decided to kill an innocent girl right before their eyes, knowing that the sisters would be duty-bound to kill him. They killed him two more times after he told them he would keep killing innocents until they killed him. After his eighth death, they came up with a potion and spell that would catch him at the moment of death and magnify it nine times.

Shadow burst into the manor hours before the new moon. Prue killed him by throwing a poker at him. At the very moment he died, Piper froze him and threw a potion at him. The sisters then read the spell, forcing Shadow to feel the pain of all nine of his deaths all at once. The pain tore him apart, vanquishing him for good.

Powers and Abilities

Active Powers

Fading: The ability to teleport in a fading manner.
Power Absorption: The ability to absorb the powers of other magical beings. When Shadow betrayed and killed Ariel, he absorbed her powers.
- Projective Levitation: The ability to levitate other beings and objects without levitating oneself. Shadow stole this power from Ariel.

Inactive Powers

Adjusting: The ability to fight through molecular powers.
Resurrection: The ability to return from the dead. Due to cats possessing nine lives, Shadow was able to resurrect himself several times after being killed.

Spells

The Charmed Ones created a spell to vanquish this feline-familiar warlock. It requires a potion that amplifies pain.

To Kill a Feline-Familar Warlock

Nine times this evil's cheated death,

Felt no pain and kept its breath.

This Warlock standing in our midst,

Let him feel what he has missed.

Notes

It is unknown if Shadow possessed the basic powers of a Warlock, as he is a former Familiar and his method of teleportation is different as well.
It is also unknown if Shadow retained the basic powers possessed by Familiars when he became a Warlock.

Deaths

Phoebe throws a spike-heeled shoe at his face in a shoe store.
Piper stabs him in the stomach with a box opener in the parking lot of a box store.
Prue mentions that she killed him in the attic.
Phoebe stabs him in the back with the tip of an umbrella.
Phoebe fights Shadow in the kitchen and kicks him over the table. He landed on top of a dinner knife Phoebe left on the floor.
Phoebe stabs him in the side with a knife after killing a girl.
Prue uses her power to throw a letter opener at him stabbing him in the stomach.
Shadow gets stabbed in the stomach with a cane in front of the Charmed Ones.
Prue throws a fire poker at him, Piper tosses a pain magnification potion at him, and the three sisters cast a vanquishing spell.

Shadow's final death was permanent because of these three things: first, Shadow had to be previously killed eight times. Second, he had to be killed for a ninth time but be frozen before his demateralization and third, the potion (in a pouch) needed to be thrown at him after which a spell has to be cast before the warlock unfreezes.