The esoteric arts have long studied the Ethereal mists as they echo our own realm. Those who delve deeply into the Ethereal Deep and return to bring its secrets are known as Aethermancers.

Among wizards, Aetherists are most often referred to as a ritualist's ritualist, for their subtle understanding of connecting to the realms beyond sight and to beckon its strange mysteries into their spellcraft. 

Resonant Codex

At 3rd level, your spellbook becomes attuned to the incorporeal world of the Border Ethereal. Your spellbook takes on a ghostly appearance, which may be a form of your choosing. As a bonus action while holding your book, you can dismiss it into the Border Ethereal. While dismissed, your spellbook hovers at a point you choose within 5 feet of you, and follows you if you move more than 5 feet in any direction. It is visibly translucent, and is intangible to objects and creatures other than you. You can use an action to resummon the book to your hand, where it appears as if from mist.

You can use this book as a spellcasting focus for your wizard spells as long as it is in your hand. If necessary, you can replace it over the course of a long rest by performing an esoteric ritual to beckon it from the Ethereal Deep. At the end of the rest, your spellbook reappears in your your hand with all of the spells recorded that you have prepared. If you enact this ritual while your book still exists, it only serves to resummon it to your hand and no other effect.

Aetheric Ritualist

Also at 3rd level, choose one first and one second level spell that lack the ritual tag you know from the wizard spell list. Your spellbook becomes attuned to those spells, and they gain the ritual tag. Each time a level in this class would grant an increase in the level of spell you can cast, you may select an additional spell to attune to in the same manner.

Esoteric Rites

Starting at 6th level, your study of the Ethereal Plane has attracted a Ghastly Spirit of the Ethereal Deep. The spirit appears from mist at the end of a long or
short rest, and uses the unseen servant stat block, except it is a Small Aberration whose visible appearance reflects an unsettling visage, such as a shadow, ghoul, or bloody footprints. You can command the Ghastly Servant in the same manner you would an unseen servant. If the spirit moves more than 30 feet away from your spellbook, it fades back within the Border Ethereal. You may expend a spell slot of 2nd level or higher as an action to resummon your Ghastly Spirit as long as you are holding your spellbook.

While performing a ritual, you may channel the spirit into its casting, consuming it in the process to complete the ritual as an action instead of its normal casting time, and adding an effect of your choosing from the list below:

• Bane from Beyond: White fire erupts around a creature you can see within 60 ft. That creature must make a Charisma saving throw or be blinded for 1 minute.
• Echoing Hex: A dolorous sound rings out in a 15 foot emanation from a point you can see. Each creature in the emanation must make a Wisdom saving throw or subtract 1d4 from each d20 test it makes within the next 1 minute. A creature may make this save again at the end of its turn.
• Pull into Mists: A faint green fog lightly obscures a 20 foot cube at a point you can see for 1 minute. A creature must expend 4 feet of movement for every 1 foot moving through the affected area.

Ethereal Transposition

At 10th level, your bond with the Ethereal Deep allows you to use its protections against harm. If a creature you can see would make a weapon attack against you, you may use a reaction to swap positions with your Ghastly Servant, which becomes the target of the attack instead.

Draw into Mist

At 14th level, you can now infuse yourself with the Ethereal Deep itself, wielding its arcane mana as your own. 
While you are concentrating on a spell or performing a ritual, you gain the benefits of the etherealness spell.