Nexus (Charmed)

A Nexus is a place equidistant from the five elements as explained in the TV series Charmed. Using this as a point of reference, it is quite possible that there could be several Nexus points of power scattered throughout the Charmed world, though rare. The one used by the Halliwell family in the Charmed series is embodied as a shadow and seen as a place of ultimate power. Phoebe Halliwell and Wyatt Halliwell, the only two people to be born in Halliwell Manor, were both strongly influenced by evil, with Phoebe becoming Queen of the Underworld and Wyatt becoming a concentrated source of evil power, enslaving the World in an alternate future.The Nexus is located in the basement of the Halliwell Manor and various demons tried to steal its power, including Cole Turner and Zankou. Each attempt is thwarted by the Charmed Ones, and it is eventually destroyed at the end of season 7.

The Shadow
The Shadow or The Woogy Man (derived from Boogie Man) is the name the Charmed Ones used to refer to the spirit within the Nexus. It was banished beneath Halliwell Manor by Penelope Halliwell, The Charmed Ones together and later by Phoebe Halliwell alone. Demons Cole Turner and Zankou, as well as the warlock Nigel, all seek to take The Shadow into themselves and take with it the power of the Nexus. The Shadow when freed has power over the entire manor and the people within, corrupting them. It is a black smoke, sometimes taking on some semblance of a form, and can speak whilst possessing no body (presumably through magic). It is destroyed along with Zankou when the sisters cast a spell, "To Destroy a Suxen (Nexus)".

Spells
To Summon the Shadow 
 * Natum ad a necral dona in tan la noc.

To Banish the Shadow
 * I am light. I am one too strong to fight.
 * Return to dark where shadows dwell.
 * You cannot have this Halliwell.
 * Go away and leave my sight.
 * And take with you this endless night.
 * (Variations to this spell were used throughout the series)

To Destroy a Suxen (Nexus spelled backwards):
 * From ancient time this power came,
 * For all to have but none to reign.
 * Take it now, show no mercy,
 * For this power can no longer be.

Production note

 * The Shadow and The Nexus were conceived originally as separate entities/artifacts, but through the years they became muddled. In season 7, the terms were used interchangeably, and the Shadow opted for a neutral party host (Leo) rather than its previous modus operandi of corrupting good with evil.

Note: The Shadow chose to possess a neutral party because it was confused as there was evil (Zankou) and good (The Charmed Ones) in the same room together. The Shadow of the Nexus only has lust for power, thus it corrupts any being it possesses, whether they be good or evil, or mortal. The Shadow and the Nexus were still two different things. When the Shadow entered Zankou, he still referred to it as the Shadow of the Nexus, then the sisters destroyed the Nexus, which is the location which embodies an absolute power. The Shadow dwells in the Nexus exactly to quench its hunger for power, as it existed only because of the power supply it gets from the Nexus. When the Nexus was destroyed using the Banish a Suxen spell, the Shadow, which was inside Zankou at the time, was destroyed at the same time because the Halliwell's Nexus' power no longer existed. That is why Penny Halliwell only created the spell to banish the Shadow back into the Nexus, precisely because the Shadow could not be destroyed without destroying the actual Nexus itself, the Shadow's dwelling place, until it was necessary to banish the Nexus altogether, as what the sisters did in season 7 with a blessing from the Elders.