Base Class: Monk
Through deep spiritual meditation and martial training, Warriors of the Spirits have formed a connection to the spirits of departed warriors. These Monks have a profound respect for the dead and the lessons that can be learned from them. They can call on these sprits for aid and become empowered in battle by channeling their power.
Level 3: Spiritual Aid
Your connection to spirits allows you to call on their aid in your times of need. You learn the Guidance Cantrip and gain Advantage of Death Saving Throws.
Level 3: Fury of the Departed
Once per turn when you hit a creature with an attack and deal damage, you can expend 1 Focus Point to call on a Spirit to deal Radiant, Necrotic, or Cold damage (your choice) to the target equal to one roll of your Martial Arts die. The affected creature’s movement speed is decreased by 15 feet until the start of your next turn.
Level 6: Spirit Channeling
You have learned to call on the aid of spirits for a wider variety of uses. You learn the spells Unseen Servant, Speak with Dead, Spirit Guardians, and Spirit Shroud. You always have these spells prepared and Wisdom is your spellcasting ability for them.
You can cast these spells by expending 1 Focus Point up to two times each. You regain your ability to cast these spells when you finish a Long Rest.
Level 11: Empowered Channeling
Your connection to the spirits you summon has grown stronger. While you are concentrating on a spell given by your Spirit Channeling feature you can use Fury of the Departed without expending a Focus Point.
Additionally, you can use Fury of the Departed a second time on your turn if you expend 1 Focus Point to do so.
Level 17: Gift of the Departed
You have achieved perfect harmony with the spirits of the departed that aid you and they’ve gifted you with greater power. When you cast a spell given by your Spirit Channeling feature you also summon spirits to protect you and your allies for 10 minutes. You and allies within 15 feet gain the effects of Half Cover and Resistance to Radiant, Necrotic, and Cold damage.
This is a Subclass I've wanted to make for a while because it feels like this kind of fantasy should be in the game officially but isn't. I hope you give it a try and enjoy it.
Note: The Level 11 Feature "Empowered Channeling" gives you the ability to use a second Fury of the Departed on your turn even if you are not concentrating on a spell from Spirit Channeling. The only thing you lose by not having Concentration is the 1 FREE use of Fury of the Departed. Otherwise the feature could be completely turned off by you losing Concentration mid-fight.