Souls

It's an ordinary item turned into an artifact via the imbuement of a soul. A soul can be imbued into anything ranging from a patch to a house. An object imbued with a soul that you own can be summoned at will, even if the object is on another place of existence, unless personally stopped by the owner/ruler/deity of the realm it is in. (1A or BA.) You can summon any owned soul as a ritual from any plane as long as you have the soul item and the owner/ruler/deity of the realm it's in personally stops it.

At first level (and higher), you can use souls in 2 ways:

1: If you have the soul of a creature with a CR greater than 3, you can kill it (from anywhere) and summon it as a Shadow (1A), under your control, communicating via telepathy. (No action required.) You can only have a number of creatures equal to your proficiency bonus summoned at once. 2: Cast a spell that you know with the soul of a creature with a challenge rating equal to or greater than double the spell level (1A).

At 6th level (and higher), you can use souls in 2 new ways:

A soul can be used in 2 new ways: 1: If you have the soul of a creature with a CR greater than 8, you can kill it (from anywhere) and summon it as a Shadow Demon (1A) under your control, communicating via telepathy. (No action required.) You can only have a number of creatures equal to your proficiency bonus summoned at once. 2: For every 12 hit points it has, you tear it into a soul piece, which instantly kills it. You can "hold" 5 pieces at a time, and spend 1 as a reaction to getting hit, healing you (or another creature within 5ft) 1d6 + your charisma modifier health.