The psychic warrior, introduced in the 3.0e splatbook Psionics Handbook and reappearing in the 3.5e Expanded Psionics Handbook, is basically a psionic-flavored gish-in-a-can. Psychic warriors were people who thought that it was cool to zap people with mind powers, but it would also be nice to be able to cut people in half with a sword. The resulting class was a half-fighter, half-psion that focused on self-buffs and boosting his own power through the roof so he could murder faster than everyone else. It worked surprisingly well, given that psionics have no physical components and therefore can be manifested in armor. It had no class features besides manifesting and bonus feats, but that was still enough to make it better than the Fighter (though in 3.5, what wasn't better than the fighter?) and make it a tier 3 class.
It returned in 5e as the Psi Warrior subclass of Fighter.
While its basic abilities to fight seem pretty bland (d8 Hit Dice, average BAB), it tends to make up for this with varying degrees of psionic cheese; they can get both fighter and psionic feats that greatly amplify their abilities over time. They get their own limited list of psionic powers that stop at 6th level, but they do get a few tricks psions can't (not without abusing psychic chirurgery anyway), and their abilities are almost entirely centered around defense, offense, and perception (so you can find your enemy better).
The initial drawback is that this class is slightly MAD, depending heavily on Wisdom for its psionic abilities and Strength and Constitution for melee combat. Dumping Dexterity is also not advisable; its only dump stats are int and cha. However, it also doesn't need an 18 in any of these scores to do well. If you're using a 25-point buy, then 16 Wisdom, 14 each in str and con, and 10 dex will get you a pretty decent ass-kicking machine.
Real trouble comes in when you start trying to figure out the right feats to get. A lot of newer players will want to get all the feats that let them do the fighter thing, and totally forget that powers more than make up for all that. Remember all those convoluted builds for barbarians to get a pounce full attack thing? Yeah, psychic warriors literally just pick psionic lion's charge when they get to 4th level, and call it a day. There's tons of little power selections like that you can pair up to the right regular fighter feats that make you a wrecking machine right out of the gate. Consider psionic lion's charge paired with Powerful Charge and Greater Powerful Charge from Miniature's Handbook, and enjoy all the d6's you start throwing down every round.
But... then you also get some really delicious psionic feats. Sure, there's the metapsionic stuff like Quicken Power, and it's not bad to have a few of those feats, but honestly, that stuff is better left to the psions and erudites out there who have the PP to spare for it. Instead, smart psychic warriors grab stuff that lets them vastly improve their combat or movement abilities: (Greater) Psionic Weapon (+2d6 to +4d6 melee damage) and Deep Impact (resolve your melee as a touch attack) are simply ridiculous. If you feel like more mobility, look up Speed of Thought (more speed in light/medium armor), Psionic Charge (change direction during charge) and Up The Walls (literally running up walls kung fu style).
A really smart build allows a psychic warrior to basically charge from up to 80-100 ft. away, taking a turn around a corner and running up a 10-ft. wall to get at the guy, and when he hits it does something like 8d6 flaming magic damage as a melee touch attack that also strokes you off... okay, maybe that last part was a little much, but you get the point. Just for a starting point, go look up a good Shock Trooper build and pair it up with the feats mentioned above.
Now, don't get too excited there, Bucky. There's a few limitations. First off, you run out of Power Points, that closes off those tricks until 8 hours of rest. You do still keep your feats, however, so pick a good set of feats for a basic form of attack, and powers that really enhance that attack routine when you need to dial it up to 11 (and/or rip off the knob). Second, your power selection is a bit limited. You can cheese out of this slightly, but you're still stuck with 6th-level and lower powers. And the cheese does cost you and/or the Telepath helping you XP, so choose wisely.
However, this class is pretty solid all the way from 1st to 20th and beyond; while the Tome of Battle may have a stronger flavor of cheese, psychic warrior builds do give them a hard run for the money, and don't smack of as much weeb as the TOB does (since you're closer to a Vancian gish on how much bullshit you can pull off daily).
The Tashalatora Build
Okay, so you're not deterred by the possible limitations? Cool. Here's how to make something a bit more broken.
In the Eberron Campaign Setting book is a feat called Monastic Training, that lets you take levels of a specific other class and still bounced back into monk without penalty; you can take this feat as a monk's bonus feat at 1st, 2nd, and other levels they get those special bonus feats.
So you start with a monk with great Wis, Dex, and Con, average Str, and whatever for Int and Cha. Level up to 2nd-level monk. Improved Grapple seems to be better regarded by most folks, since Stunning Fist's save DC gets pretty shitty against enemies with more levels/CR, but there is some use for stuns against mooks, so pick what seems better to you. At 2nd level, enjoy the use of evasion and take your bonus feat as Monastic Training (psychic warrior).
Yes, you guessed correctly, we will be taking psychic warrior directly at 3rd level. Now... flip to the Secrets of Sarlona book, pg. 119, and read the Tashalatora feat. That's right: psychic warrior will now permit you to gain monk's AC bonus, flurry, and unarmed damage. Not bad, right? You can still take Psionic Weapon and powers like metaphysical weapon, and they apply to your fist, which counts as a manufactured weapon as well as a natural one. Spare a feat for Improved Natural Attack (unarmed strike), because it's a free "size" upgrade to damage (which you can improve with other powers/feats). If you're smart, you'll get something like the scorpion kama (MIC pg. 201) that makes a magic weapon do your unarmed attack damage, then enchant the weapon even further for better stuff. Of course, you can also go back to 3.0's Savage Species for the necklace of natural weapons, which allow you to enchant the necklace to give your unarmed strike magic weapon stuff.
Otherwise? Just build the same overpowered bastard you were going to with psychic warrior.
So why the monk thing? Because you get even more synergy with Wisdom: you can basically totally dump Str, even down to 8, and just take lots of Dex, Con and Wis, and Weapon Finesse for your unarmed strike (which should probably be one of the first feats you take). Everything after that is all gravy; you can just take stuff that boosts "weapons", because your unarmed strikes count as both manufactured and natural weapons. The only issue here is, you want to find items for defense because you aren't wearing any armor. Bracers of armor are awesome, more so if the DM allows you to add enhancements as per the old 3.0 Arms and Equipment Guide. The ring of armor from "City of Splendors: Waterdeep" is another good choice, since it gives deflection AC and helps negate critical attacks. You don't really need Superior Unarmed Strike from TOB, nor do you need the monk's belt, unless you plan to dip anything that isn't monk or psychic warrior. If you do, consider getting the feat first, since it can't be turned "off" by stuff that messes with psionics and/or magic. Oddly, there's a few powers you want in Complete Psionic. As shitty as that supplement often is, it's actually a gold mine for some specific powers that were added to certain lists.
The end result, if done correctly, is that you have a monk who can basically punch for multiple d6's of damage and reach almost any enemy in a round or two (including using a few teleportation effects at higher levels). Take sustenance and psionic endure elements (the latter from Complete Psionic), and you can do the whole "never eats or drinks, isn't troubled by heat or cold" thing from certain anime sources.
Arguably, you can also do all this with a psion, though you need a lot of help to buff your melee combat ability (though it does make certain touch attacks stupidly powerful), and you're definitely gimping your access to 9th level powers doing so. A better option is the psychic rogue (from The Mind's Eye web enhancements), which allows you to make a stupendous psionic assassin build that really puts the lurk to shame: better access to powers, more skills make you useful outside of combat, and Tashalatora means you are never in need of a weapon to get your sneak attack damage against the right opponents.
If you want the DM to really throw the book at you, make your race catfolk (from Races of the Wild) and name the guy Punchcat. Enjoy...
The Vigor power gives 5 temporary HP for every PP spent on it. Share Powers means a Psicrystal also get those same Temporary HP for free. Share pain allows a willing target (like your Psicrystal) to take half the damage you would normally take. The net result of this is that vigor's effect is doubled for very minimal cost (the 3 PP to manifest Share Pain) and the user becomes very hard to kill. While not a Psychic Warrior exclusive technique, indeed they need two feats to pull it off where Psion needs none, this is quite potent on Psychic Warrior since they're a gish that wants to be in melee.
When Dreamscarred Press took advantage of psionics being Open Gaming License content to make a Pathfinder version, they gave the class actual class features in the form of Paths. A path gives a pair of bonus powers (one at 1st level, the other at 3rd), which can be manifested for free without augments by expending psionic focus and be manifested as part of an attack after level 6. Paths also give a bonus in one of three skills as well a trance (ability active when they have psionic focus) and maneuver (ability that can be used by expending said focus). Eventually a second path may be selected. It also gets to count as having full BAB for the purpose of qualifying for feats and has 4 skill points per level instead of two.
One notable archetype for the Pathfinder version of the class is Pathwalker. Pathwalker trades several bonus feats, their ability to count as having full BAB, and a late game limited use ability to have multiple trances up for maneuvers like a Path of War class. Pathwalker has a set of exclusive, discipline based, Paths them must take, instead of the normal ones, that are more narrow in application than the default ones and lack the "advanced ___ path" feat support, so this is actually a hidden nerf. What this does do however is give them 6th level powers and 6th level maneuvers from three disciplines (but they can grab higher level maneuvers with feats), making them quite versatile.
Another important archetype is the Meditant. This gives the Psychic Warrior access to monk unarmed strikes and AC in exchange for weapon and armor proficiency. In other words, it's Tashalatora without a tax of two levels and two feats. See above for what you can do with it, modify for Pathfinder, and unleash the smack on all who stand in your way.
A Psi Warrior gets d6s equal to twice their Proficiency bonus (which increase in die value as they gain levels) that can be spent to activate certain subclass powers. At 3rd level, those powers consist of Protective Field (reduce damage by a psi-die + Int modifier), Psionic Strike (add psi-die + Int modifier Force damage to a weapon attack) and Telekinetic Movement (mentally move an object or a willing creature within 30 feet). At 7th level, it gets Psi-Powered Leap for one-turn flight, and Telekinetic Thrust (Stop snickering!) to push an enemy prone or move it ten feet. Level 10 gives you resistance to psychic damage and lets you end a charmed or frightened condition on yourself, at level 15 you can create cover for your buddies, and finally, at level 18, you can cast Telekinesis, getting a bonus action to attack as long as you concentrate on the spell.
|The Classes of Pathfinder 1st Edition|
|Core Classes:||Barbarian - Bard - Cleric - Druid - Fighter - Monk |
Paladin - Ranger - Rogue - Sorcerer - Wizard
|Alchemist - Antipaladin - Cavalier |
Inquisitor - Oracle - Summoner - Witch
|Arcanist - Bloodrager - Brawler - Hunter - Investigator |
Shaman - Skald - Slayer - Swashbuckler - Warpriest
|Kineticist - Medium - Mesmerist |
Occultist - Psychic - Spiritualist
|Ultimate X:||Gunslinger - Magus - Ninja - Samurai - Shifter - Vigilante|
|The Third Party Classes of Pathfinder|
|Psionics:||Psion - Psychic Warrior - Soulknife - Wilder |
Aegis - Cryptic - Dread - Marksman - Tactican - Vitalist
|Path of War:||Stalker - Warder - Warlord - Harbinger - Mystic - Zealot|
|Akashic Mysteries:||Daevic - Eclipse - Guru - Nexus - Radiant - Rajah - Stormbound - Vizier - Zodiac|
|Spheres of Power:||Armorist - Elementalist - Eliciter - Fey Adept - Hedgewitch - Incanter |
Mageknight - Shifter - Soul Weaver - Symbiat - Thaumaturge - Wraith
|Spheres of Might:||Armiger - Blacksmith - Commander - Conscript |
Savant - Scholar - Sentinel - Striker - Technician
|Champions of the Spheres:||Prodigy - Sage - Troubadour - Dragoon - Mountebank - Necros - Reaper - Warden - Crimson Dancer|
|Pact Magic:||Pactmaker (formerly known as Medium)|