Time for me to knee jerk all over this.
Firstly, I miss the Grey boxes, those were the best, please bring them back.
A creature wielding psionic power focuses its concentration on a discipline, and in doing so, manifests a minor psionic effect. Once a creature has concentrated on a discipline, it can then tap into its reservoir of inner energy to create even greater effects.
So here it the central mechanic for psionics, that's simple and different enough
Otherworldly Power: Much ado about a little fluff. Fortunately, it does provide an easy out for DM who flat out doesn't want it in their game.
Disciplines and Psi Points:
What a strange mix of continuous and daily power. I almost expected them to refresh on a short rest.
Psionics and Magic Transparency
Oh this is going to cause problems. Ki, the other quasi-magical inner power that can be used to cast spells, doesn't have such a disclaimer. I think there should be parity here, one way or the other.
Using a Discipline
Activating a Discipline is action intensive. I guess that is to be expected. Outside of using points, and not using components, it's just like a spell. Except for that hard to parce Combining Psionic Effects bit. It needs some named examples, but I almost get what you are going for here? If you use a discipline to get water walking for 5 min, then switch up to a different discipline for mind reading, you can still water walk for the remaining time right, even if the concentration has shifted, right? In fact, how does disrupting concentration effect those spend points for timed durations abilities? It seems to imply there are exceptions to the rule of "no concentration = no lasting effects", but I don't see any such exceptions.
The Mystic
Didn't want to call it the Psion? Well I suppose they intend to combine all the psionic classes into one mass, instead of making the Psion class and an additional subclass for the Fighter, Rogue, and/or Monk. A bit of a let down.
Class Features
A bit generically simple, save for having one saving throw*
*they don't actually have one saving throw, they have a single static saving throw and a dynamic one
Strength of Mind This is kinda cool, but it's going to be overpowered when your static save is Wisdom instead of Intelligence.
Psionic Order
Finally to the meat, and they are a huge mixed bag of fresh and rotten.
Order of the Awakened
This is the "I wanted to be a Psion" option.
Mind Thrust
Why doesn't it auto-scale? It won't keep up with the cantrips otherwise, and Mystics don't get multiple attacks. (oversight, maybe?) Psi points should do things like "spend one point, you manifest fire for fire damage or crystals for weapon damage instead) Or maybe not even points, each of the disciplines could provide a different damage type to augment this.
Psychic Mind
Seems oddly limited. It's one-way communication, unless you speak the same language. Maybe it gets powered up later?
Object Reading
This is a fun non-combat power. I like it.
Conquering Mind
It's already better than
Friends at the concentration level. Damn
Friends sucks.
Exacting Query and
Occluded Mind seem like they should be reversed in level.
Broken Will DAMN. That's basically a save or die, at level 5!
Intellect Fortress
Reaction Disadvantage and you hurt them when they hit you. But remember you need Concentration to make it work. And no power point options, that's it? This Discipline sucks.
Third Eye
I take it back, if there is one thing Intellect Fortress has going for it, it's not Third Eye.
Concentration Blindsight, that's handy in the dark.
1 point for Tremorsense? (situational I guess)
1 point for Advantage on WIS checks (useful)
5 points for Truesight (Also situational, but it covers a lot more situations)
This one seems to be the least fun. It's just being able to look at stuff, within 30' of you. But no darkvision for some reason. It needs remote sensors, some form of combat utility, and pizzazz.
Order of the Immortal
Why does this not have multiple attacks? Why does the Mystic not have multiple attacks to begin with?
Durable Mind
Is it really necessary to make their concentration immune to damage? I know they are in combat but why give it to them and not any other third, half, or even full caster with a combat bent? Maybe Advantage on Concentration checks, or better armor instead?
Martial Order
Well at least they can hurt things with a sword, once a round.
Psionic Regeneration
Seriously!? I know they are called "Immortal" but you didn't actually have to make them immortal! At least not at level 3! I know there are ways to kill people besides damage, but damn, If you want one of these guys to stay down you have to out right kill them.
Celerity
Gotta go fast. Have this on, all the time, every time. Even if you want to do something else later. It combines the speedy powers of like 4 different classes and it's too good not to take right now.
Iron Durability
Great, now they are even harder to kill. At least now I have a way to make the Terminator as a Player Character. Fortunately, it lacks offensive punch, so people will want to make something else.
Psionic Weapon
Now, this right here, despite being the damage option, is probably the least powerful of all three Immortal disciplines. And consequently is at the power level I would have expected of all disciplines.
Ethereal Weapon
I think you can use this at the same time as Lethal Strike, if so, that's good. If not, it's 1 point to for at least 50% damage, which is ok.
Lethal Strike
The Only way for the Immortal to scale damage. I get the feeling this should have been the cantrip option and should auto-scale, or at least give them multiple attacks as the default.
Augmented Weapon +3 to hit for 1 min, which stacks with basically every other bonus so far (other than enchanted weapons, but who needs those?) It's like they are trying to kill bounded accuracy. It should be elemental damage or something.