Roguish Archetype
The Soul Knife
Most rogues perfect the art of deadly combat with easily concealed physical weapons. The Soulknife, however, needs no physical weapon at all, instead manifesting their deadly weapons with the power of their mind. They are excellent assassins and undercover agents, summoning a weapon in a heartbeat where an opponent expects an unarmed foe.
Psionic power is the easiest route to learning the basic tenets of this path — manifesting a soulblade. As a result, most Soulknives are either kalashtar or denizens of Sarlona, though the spark of psionic power might be found in any of the common races.
Three other traditions have evolved among elves, neither of them psionic. Rarely, elves with the Mark of Shadow have learned to manipulate the darkness to form solid blades. Meanwhile, the Umbragen of Xen'drik have discovered how to manifest blades of pure darkness through the pact of their people with the Umbra. In contrast, the Deathguard of Aerenal, channeling the power of their ancestors and the Undying Court, create blades of purest light.
Apart from these traditions, developed by Elves, there is one more, created by the Magebreeding program of House Vadalis. Completely arcane in nature, these soulknives are empowered by the weave, mimicking the psionic abilities of their fellow soulknives.
Soulblade
When you choose this archetype at 3rd level, you can form soulblades, blades forged out of pure energy, with will alone. Whenever you make an attack, you can manifest a soulblade in one or both of your hands. The soulblade is a simple melee weapon with the light, finesse, and thrown properties, it has a range of 40/80 feet, and deals 1d8 points of damage on a hit. If a soulblade leaves your hand or if you are incapacitated, it dissipates at the end of your turn.
After you attack with the blade, you can make a melee or ranged weapon attack with a second psychic blade as a bonus action on the same turn, provided your other hand is free to create it. The damage die of this bonus attack is 1d6, instead of 1d8.
The damage type of your soulblade, and additional features, depends on your chosen tradition. Choose one of the following traditions, depending on your race and origin. You cannot make this choice again.
Psionic (Any race). Your soulblade deals psychic damage. Once per turn, when you hit a creature with your soulblade, you can drive a spike of disorientating energy into their psyche. The first time it makes a saving throw before the end of your next turn, it must roll a d4 and subtract the number rolled from the save.
Your tradition modifier is Intelligence or Wisdom.
Dragonmarked (Requires Mark of Shadow subrace). Your soulblade deals psychic damage. Once per turn, when you hit a creature with your soulblade, you can cause psychic energy to surge into their mind. The target has disadvantage on the next attack roll it makes before the end of its next turn.
Your tradition modifier is Charisma.
Umbragen (Requires Drow race). Your soulblade deals necrotic damage. Once per turn, when you hit a creature with your soulblade, you can summon a sliver of the Umbra to eat away at their life's spark. If the target is missing any of its hit points, you deal an additional die of damage against that target for this attack.
Your tradition modifier is Charisma.
Deathguard (Requires Aereni Elf subrace). Your soulblade deals radiant damage. Once per turn, when you hit a creature with your soulblade, you can summon the ancestral light of the Undying Court to enshroud the target in radiance. The target has disadvantage on Dexterity (Stealth) checks and can't benefit from being invisible until the start of your next turn.
Your tradition modifier is Wisdom.
Magebred (Any race). Your soulblade deals force damage. Once per turn, when you hit a creature with your soulblade, you can split some of the energy of your soulblade. A different creature of your choice within 5 feet takes damage equal to your tradition modifier.
Your tradition modifier is Intelligence.
Speed of Will
Starting at 3rd level, your focus grants you sureness of step. Your speed increases by 10 feet, and when you use the Dash action, moving through difficult terrain costs you no extra movement until the start of your next turn.
Additionally, while you are touching a creature, you can speak telepathically to each other. You don't need to share a language with the creature to understand each other's telepathic utterances, but the creature must be able to understand at least one language.
Soul Strike
At 9th level, your soulblade’s blows can leave your opponent dazed. Whenever you use your Sneak Attack, you can send shockwaves of soul energy into the target, forcing them to make a Intelligence saving throw. On a failed save, it is stunned until the end of its next turn. The DC for this saving throw is equal to 8 + your proficiency bonus + your Tradition modifier.
You can use this feature a number of times equal to your Tradition modifier (a minimum of once), and you regain all expended uses of it when you finish a long rest.
Bladewind
Starting at 13th level, you can shatter your soulblade into a whirling tornado of soul energy, striking all nearby foes. As an action, you can use your soulblade to make weapon attacks against every opponent within 15 feet of you.
You can use this feature a number of times equal to your Tradition modifier (a minimum of once), and you regain all expended uses of it when you finish a long rest.
Knife to the Soul
Starting at 17th level, you can overwhelm a creature's higher brain functions with a strike. As a reaction to using your Sneak Attack, you can cast feeblemind on the target of that attack. The DC for this saving throw is equal to 8 + your proficiency bonus + your Tradition modifier. When cast in this way, feeblemind does not count as a spell and any damage dealt by it deals your soulblade damage type.
Once you use this feature, you can't use it again until you finish a long rest.