This is an adaption of the Mystic class, which is not feasible as a standalone class currently. It is way more balanced and quite interesting, specifically for rouges.

To be more precise, this is an adaption of the "Imortal" subclass of the mystic. It is highly advised to have a look at the Mystic UA class.

Balancing wise, this subclass has less options and less capabilities. There are no regulations regarding the amount of Psi Points you may spend, but you may not get them back. You can only have one feature active at the same time. Also, you will have to sacrifice points to enhance your int-score, to have more power full abilities.

All credits for the specifics of the Features go to WOTC.

Psionic Disciplines

A psionic discipline is a rigid set of mental exercises that allows a mystic to manifest psionic power. A mystic masters only a few disciplines at a time.

Each discipline costs a certain amount of psi points to activate. These points are consumed when the ability is activated. Only one ability can be activated at a time, in addition to your psionic focus. Even if an ability says, that you have to spend x amount of psi points, you can spend up to 7 points on a single ability. However, if not specified otherwise, this does not change the effects.

Each discipline has a passive ability called "psionic focus", which has no activation cost. You can have one of these abilities active at any time. Changing the focus costs one action.

Some abilities require additional concentration. The same rules apply to these as to spells. The time indicates how long the ability remains active with concentration maintained. While you have an ability with concentration active, you cannot activate another ability until you cancel the concentration with a bonus action. 

You gain 2 Disciplines if you choose this subclass and again at 6th, 10th and 14th level.

Adaptive Body

You can alter your body to match your surroundings, allowing you to withstand punishing environments. With greater psi energy, you can extend this protection to your fellow teammates.

Psychic Focus. While focused on this discipline, you don’t need to eat, breathe, or sleep. To gain the benefits of a long rest, you can spend 8 hours engaged in light activity, rather than sleeping during any of it

Bestial Form

Just as you get to know more of the talent that lies dormant within you, you learn not only to transform yourself completely, but to transform parts of yourself into your favorite animals.

The gils of a fish, the wings of a bird or the thick skin of a bear. Parts of your body become what you like most.

Psychic Focus. While focused on this discipline, you have advantage on Wisdom (Animal Handling) checks. 

Brute Force

You augment your natural strength with psionic energy, granting you the ability to achieve incredible feats of might. Your hits become harder, your jumps further your muscles harder. 

Psychic Focus. While focused on this discipline, you have advantage on Strength (Athletics) checks.

Celerity

You channel psionic power into your body, honing your reflexes and agility to an incredible degree. The world seems to slow down while you continue to move as normal.

Psychic Focus. While focused on this discipline, your walking speed increases by 10 feet.

Corrosive Metabolism

Your control over your body allows you to deliver acid or poison attacks.

Psychic Focus. While focused on this discipline, you have resistance to acid and poison damage.

 

Diminution

You manipulate the matter that composes your body, drastically reducing your size without surrendering any of your might.

Psychic Focus. While focused on this discipline, you have advantage on Dexterity (Stealth) checks.

Giant Growth

You infuse yourself with psionic energy to grow to tremendous size, bolstering your strength and durability.

Psychic Focus. While focused on this discipline, your reach increases by 5 feet.

 

Iron Durability

You transform your body to become a living metal, allowing you to shrug off attacks that would cripple weaker creatures.

Psychic Focus. While focused on this discipline, you gain a +1 bonus to AC.

Mental Disquite

As you learned to use your inner, psychic strength, you feel yourself being quite restless. You feel that it is hard to loose your focus and rest. Sometimes, you just can't loosen up enough, to rest successfully in a short period of time.

When finishing a short rest, you have to succeed a DC10 + (amount of Psi Points spend divided by 3) or regain no expended Psi Points.

Psionic Restoration

You wield psionic energy to cure wounds and restore health to yourself and others.

Psychic Focus. While focused on this discipline, you can use a bonus action to touch a creature that has 0 hit points and stabilize it.

Psionic Weapon

You have learned how to channel psionic energy into your attacks, lending them devastating power.

Psychic Focus. Whenever you focus on this discipline, choose one weapon you’re holding or your unarmed strike. When you attack with it while focused on this discipline, its damage is psychic and magical, rather than its normal damage type.

Base Discipline

As you choose this Subclass, you gain one Discipline, which doesn't count towards your other disciplines chosen.

Nomadic Chameleon

You create a screen of psychic power that distorts your appearance, allowing you to blend into the background or even turn invisible.

Psychic Focus. While focused on this discipline, you have advantage on Dexterity (Stealth) checks.

 

Third Eye

You create a third, psychic eye in your mind, which you cast out into the world. It channels thoughts and knowledge back to you, greatly enhancing your senses.

Psychic Focus. While focused on this discipline, you have darkvision with a range of 60 feet. If you already have darkvision with that range or greater, increase its range by 10 feet.

Psionic Talents

A psionic talent is a minor psionic effect you have mastered. At 3rd level, you know one psionic talent of your choice. You learn additional talents of your choice at higher levels; when that number goes up for you, choose a new talent.

Psionic talents are minor abilities that require psionic aptitude but don’t drain a mystic’s reservoir of psionic power. Talents are similar to disciplines and use the same rules, but with three important exceptions:

• You can never use your psychic focus on a talent.
• Talents don’t require you to spend psi points to use them.
• Talents aren’t linked to Mystic Orders.

Beacon

As a bonus action, you cause bright light to radiate from your body in a 20-foot radius and dim light for an additional 20 feet. The light can be colored as you like. The light lasts for 1 hour, and you can extinguish it earlier as a bonus action

Blade Meld

As a bonus action, a one-handed melee weapon you hold becomes one with your hand. For the next minute, you can’t let go of the weapon nor can it be forced from your grasp.

Blind Spot

As an action, you erase your image from the mind of one creature you can see within 120 feet of you; the target must succeed on a Wisdom saving throw, or you are invisible to it until the end of your next turn.

Delusion

As an action, you plant a false belief in the mind of one creature that you can see within 60 feet of you. You can create a sound or an image. Only the target of this talent perceives the sound or image you create.

If you create a sound, its volume can range from a whisper to a scream. It can be your voice, someone else's voice, a creature's roar, a musical instrument, or any other sound you pick. It lasts for 1 minute.

If you create an object, it must fit within a 5- foot cube and can’t move or be reflective. The image can't create any effect that influences a sense other than sight. The image lasts for 1 minute, and it disappears if the creature touches it.

Energy Beam

As an action, you target one creature you can see within 90 feet of you. The target must succeed on a Dexterity saving throw or take 1d8 psychic damage. It perceives the damage as any other type of your choice, using this damage for resistance, immunities and vulnerabilities.

The talent’s damage increases by 1d8 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8).

Light Step

As a bonus action, you alter your density and weight to improve your mobility. For the rest of your turn, your walking speed increases by 10 feet, and the first time you stand up this turn, you do so without expending any of your movement if your speed is greater than 0.

Mind Slam

As an action, you target one creature you can see within 60 feet of you. The target must succeed on a Constitution saving throw or take 1d6 force damage. If it takes any of this damage and is Large or smaller, it is knocked prone.

The talent’s damage increases by 1d6 when you reach 5th level (2d6), 11th level (3d6), and 17th level (4d6).

Mind Thrust

As an action, you target one creature you can see within 120 feet of you. The target must succeed on an Intelligence saving throw or take 1d10 psychic damage.

The talent’s damage increases by 1d10 when you reach 5th level (2d10), 11th level (3d10), and 17th level (4d10).

Mystic Charm

As an action, you beguile one humanoid you can see within 120 feet of you. The target must succeed on a Charisma saving throw or be charmed by you until the end of your next turn.

Mystic Hand

You can use your action to manipulate or move one object within 30 feet of you. The object can’t weigh more than 10 pounds, and you can’t affect an object being worn or carried by another creature. If the object is loose, you can move it up to 30 feet in any direction.

This talent allows you to open an unlocked door, pour out a beer stein, and so on.

The object falls to the ground at the end of your turn if you leave it suspended in midair.

Psychic Hammer

As an action, you try to grasp one creature you can see within 120 feet of you, with a hand crafted from telekinetic energy. The target must succeed on a Strength saving throw or take 1d6 force damage. If it takes any of this damage and is Large or smaller, you can move it up to 10 feet in a straight line in a direction of your choice. You can’t lift the target off the ground unless it is already airborne or underwater.

The talent’s damage increases by 1d6 when you reach 5th level (2d6), 11th level (3d6), and 17th level (4d6).

Immortal Durability

Starting at 2nd level, your hit point maximum increases by 1 for every level.

Surge of Health

Starting at 6th level, you can draw on your psychic focus to escape death’s grasp. As a reaction when you take damage, you can halve that damage against you. Your psychic focus immediately ends if it’s active, and you can’t use it until you finish a short or long rest.

You can’t use this feature if you can’t use your psychic focus.

Psionic Resilience

Starting at 10th level, your psionic energy grants you extraordinary fortitude. At the start of each of your turns while fighting, you gain temporary hit points equal to your Intelligence modifier (minimum of 0) if you have at least 1 hit point. Those temporary hit points disappear after the fight.

Immortal Will

Starting at 14th level, you can draw on your reserves of psionic power to survive beyond death. At the end of your turn while at 0 hit points, you can spend 5 psi points to immediately regain a number of hit points equal to you druid level + your Constitution modifier.