Most of the time, when a cleric casts a spell, they are channeling some divine energy from their deity, manifesting their god's will in the world. But clerics who are devoted to the Athar philosophy know that this mediation is unnecessary. It is not essential to devote yourself to a god to access divine power — every person has the potential within them to access it for themselves.
However, the nature of this divine energy remains opaque. Even the Athar do not know explicitly what forces they call upon when they use divine magic. Theories abound: some say it is a pool of energy that the gods jealously guard. Others say that it is the simple power of belief in your own worthiness as a life that turns you into a font of divine energy for yourself, or that adherence to the Athar philosophy itself creates this pool. Some imagine that the divine energy flows from the same place that powers the entities that power warlocks — putting the Athar in perhaps dangerous company. The Athar study these theories passionately, eager to shed light onto the darkness, but for now, the answer remains elusive (and many Athar are quick to blame the existing gods for the elusiveness of understanding their power). Thus, they call the source of their power "The Great Unknown."
The Great Unknown powers every divine spell cast by any Athar cleric, druid, or paladin who devotes themselves to it. It doesn't seem to prohibit or disallow any spell or any kind of magic. An Athar cleric with the Tempest domain calls upon the power of the Great Unknown to create destructive storms and blasts of wind and lightning. An Athar paladin who swears the Oath of the Ancients calls upon the Great Unknown to master the forces of nature and protect life. An Athar druid who joins the Circle of the Moon calls upon the Great Unknown to transform his body into a wild beast. Not all Athar members call upon the Great Unknown (plenty of Athar druids, for instance, revere the concept of nature as the origin of all divine power), but those who do are at the forefront of exploring what this divine source of energy is.
And among those who are exploring, the Athar clerics are at the forefront. In fact, the clerics of the Athar have developed a unique divine domain, exclusive to them and to the Great Unknown. This domain is known as the Unknown Domain.
The Great Unknown is a source of many different divine energies, and those who follow the Athar teachings closely and earn the respect of their superiors can access the domain unique to that source: the Unknown Domain. The clerics who know of the Unknown Domain are considered "parters of the veil," those who are looking beyond the surface world toward the origin of all divine energy, to gain insights into the creation and transformation of the planes themselves. As such, the Unknown Domain gives power and protection over planar beings of various stripes, making the clerics with this domain quite adept at dealing with most planar natives. It also has a handful of divination effects, which allow the Athar to gain knowledge from the Unknown.
Unknown Domain Spells
|1st||detect good and evil, protection from good and evil|
|3rd||augury, magic weapon|
|5th||magic circle, protection from energy|
|9th||dispel evil and good, planar binding|
At 1st level, you learn the languages of Abyssal, Celestial, Deep Speech, Infernal, Primordial, and Sylvan.
Also at 1st level, you can defy others. When you make a Wisdom or Charisma saving throw, you can use your reaction to gain advantage on the save.
You can use this feature a number of times equal to your Wisdom modifier (a minimum of once). You regain all expended uses when you finish a long rest.
Channel Divinity: Turn Immortals
Starting at 2nd level, you don't gain an additional kind of Channel Divinity. Instead, your Turn Undead ability expands: it also works against fiends, celestials, constructs, elementals, fey, and aberrations, as well as undead.
At 5th level, when you would normally acquire Destroy Undead, you instead acquire the Convert Immortals ability.
Starting at 5th level, when an undead, fiend, celestial, construct, elemental, fey, or aberration fails its saving throw against your Turn Immortals feature, the creature can be, at your option, instead charmed by you for 1 minute or until it takes damage. While it is charmed by you, it is friendly to you and other creatures you designate.
Channel Divinity: Additional Domain
At 6th level, you gain another use of your Channel Divinity. You can select any other domain's 2nd-level Channel Divinity feature and add it to the list of Channel Divinity abilities you have access to.
Starting at 8th level, you add your Wisdom modifier to the damage you deal with any cleric cantrip.
Your New God
At 17th level, you gain the ability to command immortals. While creatures are charmed by your Convert Immortals feature, you can take a bonus action on your turn to verbally command what each of those creatures will do on its next turn.