This is a 5e port of the shadowcrafter variant of my soulcrafter class from 3.5, which was itself a fix for the soulknife class published in the Expanded Psionics Handbook. Your criticism and suggestions are requested and appreciated.
SHADOWCRAFT ASSASSIN: A ROGUE ARCHETYPE
Starting at 3rd level, your sneak attack damage dice deal [psychic] damage. You can now only deliver your sneak attack when wielding a shadowcraft weapon.
Starting at 3rd level when you select this archetype, you can use an object interaction to manifest a shadowcraft, which appears as a pitch-black object wreathed in shadows. You can maintain up to three shadowcrafts at a time, but a shadowcraft item vanishes one round after it leaves your immediate possession.
A shadowcraft must be a solid object or collection of related objects of no more than Medium size, and must be of a form and material that you have seen before. It can be any weapon or armor, a mundane piece of gear, or a vehicle or structure such as a coracle, cart, or tent. If you manifest a ranged weapon it can manifest its own ammunition. If you manifest a vehicle or structure, it appears properly outfitted with normal furnishings (a vessel may contain oars and shipboard weapons or a house may contain furniture and cookware) but these furnishings vanish one round after being removed from the vehicle or structure. To manifest a weapon, armor, vehicle, or tool kit, you must be proficient in its use.
A shadowcraft item always manifests either properly equipped on your person, in your hand, or in an unoccupied space adjacent to you. Manifesting a shadowcraft can never be an offensive or defensive action. This means that you cannot manifest a shadowcraft in such a way as to make an attack, trap or enclose a creature (even yourself), interrupt or impair a creature's action, or damage or ram an object or vehicle. Manifested shadowcrafts must be properly supported by their environment. You cannot crush something by manifesting a house on top of it or smash foes by manifesting an anvil in midair and making it fall on them, for example. You may only manifest shadowcrafts during your turn; you cannot ready an action to manifest a shadowcraft. You cannot manifest poisons or other biological substances. Your shadowcrafts cannot be used as spell components. Your shadowcrafts are obviously supernatural and cannot be mistaken for normal objects.
At 3rd level, you can manifest a shadowcraft that is a magic item with a Tier 1 property (see below). To manifest a magic item, you must be able to meet any prerequisites for its use and attunement. To manifest a spell scroll, you must know the spell and be able to cast it (it must be one of your spells known or you must have written it into a spellbook you own). If the item requires attunement, you are attuned to it. This augmented shadowcraft vanishes one round after it leaves your immediate possession, or whenever you complete a long rest.
You regain your use of this ability whenever you complete a long rest.
Upon reaching 9th level, you can maintain up to four shadowcrafts and can manifest shadowcrafts of up to Large size, such as a chariot, rowboat, or shack. At 13th level, you can maintain up to five shadowcrafts and can manifest shadowcrafts of up to Huge size, such as a wagon, raft, or small house. At 17th level, you can maintain up to six shadowcrafts and can manifest shadowcrafts of up to gargantuan size, such as a galley, sailing ship, or mansion.
Improved Shadow Augment
At 9th level, you can use Shadow Augment twice and gain access to Tier 2 properties. At 13th level, you can use Shadow Augment three times and gain access to Tier 3 properties. At 17th level, you gain access to Tier 4 properties.
Spoiler: Shadow Augment Tiers
A Tier 1 Shadow Augment can have any one of the following effects:
• Duplicate any uncommon weapon, armor, potion, or scroll;
• Duplicate any common magic item;
• Grant proficiency with one skill;
• Grant darkvision.
• The shadowcraft is one size larger than your normal size limit.
A Tier 2 Shadow Augment can have any one of the following effects:
• Duplicate any rare weapon, armor, potion, or scroll;
• Duplicate any uncommon ring, rod, or wondrous item;
• Grant constant advantage with one skill;
• The shadowcraft does not vanish after it leaves your possession.
A Tier 3 Shadow Augment can have any one of the following effects:
• Duplicate any very rare weapon, armor, or potion;
• Duplicate any uncommon staff or wand;
• Duplicate any rare ring, rod, or wondrous item;
• Grant proficiency with one saving throw;
• The shadowcraft is invulnerable to all forms of harm.
A Tier 4 Shadow Augment can have any one of the following effects:
• Duplciate any legendary weapon, armor, or potion;
• Duplicate any rare staff or wand;
• Duplicate any very rare ring, rod, or wondrous item;
• Grant constant advantage with one saving throw.
If you duplicate a magic item, you can choose only from among magic items listed in the Dungeon Master's Guide plus any other sources that your DM makes available to you. You cannot duplicate bardic instruments or magic items that permanently set or improve ability scores. To manifest a magic item, you must be able to meet any prerequisites for its use and attunement. To manifest a spell scroll, you must know the spell and be able to cast it (it must be one of your spells known or you must have written it into a spellbook you own).
At 13th level, you learn to make a special attack when you are wielding a shadowcraft weapon. As an Attack action, you direct your shadowcraft weapon (or ammunition if it is a ranged weapon) to split into multiple parts or fire multiple pieces of ammunition, making one weapon attack against each foe you threaten (or each foe within 30 feet if using a ranged or thrown weapon).
You can use this ability twice. You regain your uses of this ability whenever you complete a short or long rest.
Upon reaching 17th level, you gain access to Tier 4 properties when using Improved Shadow Augment.