Way of the Yin and Yang monks utilize two weapons, imbued with the powers of the dark and the light, respectively. The use of these weapons gives these monks access to powerful magic.

Yin and Yang Weapons

At 3rd level, you gain the ability to imbue weapons with the powers of the yin and the yang. You may, during a long rest, imbue the power of the yin or the yang into a weapon (one long rest will let you imbue the yin into one weapon, and the yang into another).

You may only wield these weapons together, and a weapon imbued with the yin cannot also be imbued with the yang, and vice versa. The weapon imbued with the yin does an extra 1d4 necrotic damage on a hit. The weapon imbued with the yang does an extra 1d4 radiant damage on a hit.

Additionally, every time you attack, you must alternate which yin yang weapon you use (i.e. If you use your yin weapon first, your next attack must be with the yang weapon, etc.). 

Dual Weapon Fighting

At 3rd level, you gain the Fighting Style Two-Weapon Fighting: When you engage in two-weapon fighting, you can add your ability modifier to the damage of the second attack.

Bodily Balance

At 6th level, whenever you hit with your yin weapon, you deal twice the amount of necrotic damage (i.e. if you did 3 necrotic damage, then do 3 more necrotic damage). Whenever you hit with you yang weapon, heal as much HP as you did radiant damage (i.e. if you did 3 radiant damage, then heal 3 HP).

Additionally, you are resistant to both radiant and necrotic damage.

Flurry of Slashes

At 11th level, immediately after you take the Attack action on your turn, you can spend 5 ki points to make two attacks, one with each yin yang weapon, as a bonus action.

Duality

At 17th level, instead of doing 1d4 extra damage (either radiant or necrotic) with your yin yang weapons, you now do 1d6 extra damage.

Also, you may spend 1 ki point to gain the effects of Darkness, centered on your yin weapon.You may also spend 1 ki point to gain the effects of Light, centered on your yang weapon.

Unity

At 17th level, whenever a creature dies, if it was damaged by both your yin and your yang weapons, any number of target creatures in a 30ft radius of you heal 1d6 HP, or any number of target creatures in a 30ft radius of you take 1d6 necrotic damage.