Insanity Domain

Whenever a Cleric has given up all hope and has stopped believing in their god, a corruptible force might overtake them. This would be the work of Tharizdun, using Voidharrow to influence the broken to follow and pledge their loyalty to him. For those who prove more capable than others, he allows to obtain more power through his power at the Voidharrow. For those that don’t meet his expectations... Well, it’s best not to say. 

Bonus Proficiency

When you choose this domain at 1st level, you gain proficiency with heavy armor and martial weapons.

Blinding Madness

When you choose this domain at 1st level, you can wave void energy into the eyes of attacking creatures. When you are attacked by a creature you can see within 30ft, you can use your reaction to force that creature to roll a Wisdom saving throw. On a failed save, they have disadvantage on the triggering attack as void energy obscures their vision. On a successful save, they ward of the dark forces influence and can make the attack as normal. Creatures immune to being blinded are immune to this effect.
You can use this feature a number of times equal to your Wisdom modifier (a minimum of once).
You regain all expended uses when you finish a long rest.

Channel Divinity: Corruptive Thoughts

Starting at 2nd level you can use a reaction to present your holy symbol when a creature within 60 feet of you casts a spell or makes a melee attack, you can use a reaction to force it to make a Wisdom saving throw. The creature must make a Wisdom saving throw. If they succeed, they continue their attack. If they fail they will start to act mad, being tormented by their own mind for a whole minute. The creature cannot cast concentration spells during this time, and will take 1d6 Physic damage at the start of their turn for a minute. The affected target can make the saving throw again at the end of their turn, ending the effect on a success.

Bonded with the Void

Once you reach 6th level, Your body has become familiar with the properties of Voidharrow after having spent periods of time in direct contact with it. From it you gain resistance to Necrotic and Psychic Damage.

Channel Divinity: Wasting Away

Your connection to Tharizdun has grown stronger. For being faithful to him, he allows you to tap into the power of Voidharrow. Starting at 8th level you can use a bonus action to present your holy symbol. When you damage a creature with a melee weapon attack they become inflicted. At the start of their next turn they take (1d6 + WIS Modifier) Necrotic damage and lose half of their speed for that turn. This damage increases to (2d6 + WIS Modifier) at 14th level.

Aura of Death

At 17th level, Tharizdun has imbued you with some of his power. As an action, you can present your holy symbol to all creatures within a 15ft sphere. Any creature inside the radius must make a Wisdom saving throw as their worst memories and fears become vivid to their senses. A creature takes 5d6 Necrotic Damage on a failed save, or half as much on a successful one. Friendly creatures automatically save, and the you take 2d8 psychic damage for every creature affected. You can use this feature once. You regain all expended uses when you finish a long rest.