The Aether twin is a fighter who never fights alone. They can be a rare breed of magic user who's given up their ability to cast spells in order to be able to summon a spectral copy of themselves in order to control the battlefield and keep their back covered at all times.

The Soul

The Fifth element is usually transcendental, spiritual, different. Metaphysical, even; the Greeks called it Quintessence (fifth-element); some think of it as spirit, or Aether, the ever-pervasive meta-substance which exists in all matter; the Japanese think of it as Mu, or emptiness, void, without; Captain Planet calls it Heart; I like the interpretation that Milla Jovovich with Orange Hair... Love is the Fifth Element.

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NOTES: 
- This subclass was created prior to the release of Echo Knight created by Matt Mercer, this 3rd revision is incorporating the abilities of mine and his subclass to really make whoever uses this subclass shine! 
- PLEASE keep in mind, I balanced this subclass by using references to other subclasses, feel free to make a "house rule" if any of the abilities feel strong or weak. 
- Feedback and Suggestions are always appreciated! 

Direct Inspiration: Reddit User: u/SethBlackwood
Art Credit: Goran Josic - On Artstation

Arcane Splinter

3rd-level Aether Twin feature

You can use a bonus action to magically manifest an splinter of yourself in an unoccupied space you can see within 15 feet of you. This splinter is a magical, translucent, gray image of you that lasts until it is destroyed, until you dismiss it as a bonus action, until you manifest another splinter, or until you’re incapacitated.

Your splinter has AC 14 + your proficiency bonus, 1 hit point, and immunity to all conditions. If it has to make a saving throw, it uses your saving throw bonus for the roll. It is the same size as you, and it occupies its space. On your turn, you can mentally command the splinter to move up to 30 feet in any direction (no action required). If your splinter is ever more than 30 feet from you at the end of your turn, it is destroyed.

You can use the splinter in the following ways:

• As a bonus action, you can teleport, magically swapping places with your splinter at a cost of 15 feet of your movement, regardless of the distance between the two of you.
• When you take the Attack action on your turn, any attack you make with that action can originate from your space or the splinter's space. You make this choice for each attack.
• When a creature that you can see within 5 feet of your splinter moves at least 5 feet away from it, you can use your reaction to make an opportunity attack against that creature as if you were in the splinter's space.
• As a bonus action/ action, your splinter may use the Dash, Help, Hide, Ready action, and Interact with an Object actions.

Unified Mind

At 3rd level, you may see through your splinter and you may gain advantage on Wisdom (perception) and Intelligence (investigation) checks if both you and your splinter are within 10ft of each other and looking at or for the same thing. 

Additionally, you can heighten your splinter's fury. Whenever you take the Attack action, you can make one additional melee attack from the splinter's position.

You can use this feature a number of times equal to your Constitution modifier (a minimum of once). You regain all expended uses when you finish a long rest.

Splinter's Avatar

7th-level Aether Twin feature

You can temporarily transfer your consciousness to your splinter. As an action, you can see through your splinter's eyes and hear through its ears, and speak through it. During this time, you are deafened and blinded. This Splinter is an ethereal-like copy of yourself that looks and sounds like you, but is distinguishable from you if you are present. You can sustain this effect for up to 10 minutes at a time, and you can end it at any time (requires no action). While your splinter is being used in this way, it can be up to 1,000 feet away from you without being destroyed.

Aether Ascension

10th-level Aether Twin feature

You can make your splinter throw itself in front of an attack directed at another creature that you can see. Before the attack roll is made, you can use your reaction to teleport the splinter to an unoccupied space within 5 feet of the targeted creature. The attack roll that triggered the reaction is instead made against your splinter .

Once you use this feature, you can’t use it again until you finish a short or long rest.

Additionally the distance between you and your Splinter is increased from 30ft to 60ft. 

Requital Redemption

15th-level Aether Twin feature

You’ve learned to absorb the fleeting magic of your splinter and channel it. When an splinter of yours is destroyed by taking damage, you can roll a d10 and on a roll of 9 or 10 the splinter is restored. You can only restore a splinter a number of times equal to half your proficiency bonus (round down) per long rest.
(NOTE: The same splinter cannot be restored twice)

Additionally, when a Splinter of yours is destroyed by taking damage, you can gain a number of temporary hit points equal to 2d6 + your Constitution modifier, provided you don’t already have temporary hit points.
You can use this feature a number of times equal to your Constitution modifier (a minimum of once). You regain all expended uses when you finish a long rest. 

Trinity

18th-level Aether Twin feature

You can use a bonus action to create two splinter's with your Arcane Splinter feature, and these splinter's can coexist. If you try to create a third splinter, the previous two splinters are destroyed. Anything you can do from one splinter's position can be done from the other’s instead.