School of Psychomancy

Psychomancy is a sub-discipline of necromancy that while more distant from common necromancer stereotypes is just as feared and engages in practices that are not evil by themselves but still very uncanny. Psychomancy is the study of the soul, whether living or disembodied, or existing as incorporeal undead. Psychomancers can augment the souls of their allies, recruit disembodied souls such as ghosts, and alter one's own soul—or rather one's own self.

Soul Collector

Your curiosity into souls has attracted attention from disembodied souls around you. Starting at level 2 you learn to enlist souls of the dead into your service. Such souls can have a variety of motivations such as ghosts who wish continue an adventure before departing or maybe you managed to find souls destined for the lower planes who are eager to somehow repent for their sins. You begin with one soul "assistant" that found you, or was given to you.

Souls that can be recruited can come from friendly ghosts, recently slain creatures, or from magical objects that have souls trapped inside them; but the soul must be willing to join you. You can encounter opportunities throughout your journey to add more souls to your collection with a Charisma (persuasion) check + your Intelligence modifier, but cannot exceed a number equal to half your wizard level. Souls can be vulnerable to magic or certain monsters, so it is important to keep them safe. You may store your souls inside a magical object or arcane focus; if the item is destroyed, the souls are released but may still linger around you.

Any ghosts or other incorporeal undead who join you cease being counted as ghosts or any other incorporeal undead.  Joining you has given them new purpose and they shed their ectoplasmic "bodies".  

Embody Souls

At level 6, whenever you cast a spell that creates undead such as animate dead, you can animate corpses by having your soul companions possess them. Any undead created this way add your Intelligence modifier to its Intelligence and Constitution scores, adds your wizard level to its hit point maximum and uses your proficiency bonus to its weapon damage rolls. If you have more than three such undead active at a time, you must use an action to command them. Due to higher intelligence, your undead can receive complex or vague commands such as "spy on the lich and report back to me before midnight", and can communicate with you telepathically regardless of language. You may use a bonus action to command your souls to retreat from their corpses.

You may also store souls within your own body. They cannot possess your or read your mind, but they can communicate with your telepathically and vice versa.  You may consult your souls for information if they are inside you, you gain advantage on Intelligence (history) checks pertaining to the soul's past while alive.

Empower Souls

Starting at level 10 you may touch a creature who has a soul and give it advantage on Charisma saving throws, advantage on saving throws against being charmed, frightened, or possessed, and immunity to any enchantment spells unless the creature willingly allows it. This effect lasts for 1 hour and can be used a number of times equal to your Intelligence modifier. Once you use this feature, you cannot use it on the same creature for 24 hours.

Additionally, whenever you make a death saving throw, you add a bonus to your rolls equal to the number of souls you gathered. If you die, one of your recruited souls of your choice can inhabit and animate your corpse but is taken control by the DM, and it's Charisma, Wisdom, and Intelligence score are set at 10 and counts as an undead creature. Resurrection spells can only work if the souls inside leave the corpse.

Master of Souls

At level 14, you have become a master soul to your recruited souls. You can use an action to link your soul and all your other souls together to merge your abilities. During the time you are linked you can  have skill proficiency in your choice of five skills when using this feature, you can receive memories from your souls and if you are not careful—even some personality traits. Your mind and brain respond in turn and your cognitive capabilities are greatly boosted, you gain advantage on all Intelligence checks. This feature lasts for 10 minutes and you may not use it until your finish a long rest.

Also, If you cast a spell that displaces your soul such as magic jar or astral projection, a recruited soul of your choice can take over your body during the duration of the spell.