Aside from cursed tools and cursed corpses, any item that holds cursed energy is a cursed object. Cursed objects are graded the same way as cursed tools, by the strength of the cursed energy they contain, and the most dangerous are ranked special grade.
Registered Cursed Objects
Sukuna’s Fingers. The twenty fingers of the King of Curses’ original body. Each holds immense cursed energy and draws cursed spirits to it the moment it is unsealed - every cursed spirit with a Wisdom score of 8 or lower within 1,000 feet is compelled to try to consume it. A cursed spirit that eats one becomes a finger bearer, gaining +2 to its Strength, Dexterity, Constitution, and Charisma scores (including their maximums) and +5 to its maximum Cursed Energy per finger. If a creature that is not a construct or cursed spirit swallows one, it must make a DC 27 Constitution saving throw or die instantly, the finger expelled unharmed. On a success, the King of Curses begins to incarnate within it, and it must then make a DC 27 Wisdom saving throw. On a failure it loses control of its body; on a success it holds on through sheer will (and gains a level in a class if it had none). A creature that resisted must repeat the DC 27 Wisdom save every time it rolls initiative or be controlled for 1 minute.
Cursed Womb: Death Painting. Cursed wombs that carry human DNA and can incarnate when swallowed by a humanoid. A humanoid that ingests one must make a DC 23 Constitution saving throw. On a failure it becomes a Death Painting with a physical body, losing control of itself but keeping its creature type; on a success it becomes a Living Vessel. Either way, it gains a level in a class if it had none.
Prison Realm. A “taboo” cursed object: a living barrier said to be able to seal anything. Placed on the ground with the command “Gate Open,” it seizes a target that has stayed within 15 feet for 1 minute - the target becomes restrained and incapacitated as it is ensnared - and the command “Gate Close” seals it away indefinitely in a timeless pocket dimension. It cannot be used again until whatever is inside destroys itself, and only something that negates cursed techniques, such as the Inverted Spear of Heaven, can break it open.
Creating Cursed Objects
Turning others into cursed objects. During a long rest you can form a binding vow with a willing creature to turn them into a cursed object, as long as one of their body parts is intact and imbued with their cursed energy. They become a cursed object of a grade equal to their power.
Turning yourself into a cursed object. As a bonus action for 20 Cursed Energy, you can transform part of your body into a cursed object.
Split objects. You can spread a single person across several objects by using multiple matched body parts - a set of fingers or eyes, say - dividing their cursed energy as evenly as possible. A single object needs at least 25 cursed energy to allow incarnation on its own; if none holds that much, a creature must consume enough of the set to total 25 (or your maximum, whichever is lower). Destroyed objects do not pass their energy to the rest, and if too few remain to incarnate even together, the soul loses its foothold and moves on.
Forcing someone to eat a cursed object. As an action, choose a creature within reach and make a Strength (Athletics) check contested by its Strength (Athletics) or Dexterity (Acrobatics). On a success, you force it to swallow the object.
Being a Cursed Object
A cursed object is aware of its surroundings but cannot interact with anything and does not count as a creature. It is immune to all damage, even damage that would normally bypass immunity, and it draws cursed spirits toward it based on the strength of its cursed energy.