This +3 magical Hand Crossbow has two configurations. In either configuration, when you roll a 20 on your attack roll with this magic weapon, the target is immediately put under the effects of Hunter's Mark and takes an extra amount of psychic damage equal to your proficiency bonus. 
This crossbow, regardless of configuration, can shoot six bolts before needing either your action or bonus action to reload. 

It's first configuration it is a simple hand crossbow, that deals Force damage instead of piercing, and you can expend 1 of its charges to attempt to blind a target for 1 round. (Dex Save 14). Additionally you can expend 1 charge do deal an extra 1d4 force damage to your target. 

The Witchbane's Eye's second configuration turns it into a mechanical spider turret. You can use a bonus action to command the turret to move up to 20 ft and fire a single bolt, dealing 1d6 Force damage. Additionally you can expend one of its charges to cast Arcane Eye, seeing through the large blue gem in the Witchbane's Eye. You may also attach one set of tools you are proficient with to the Witchbane's Eye, allowing you to use your bonus action to allow the mechanical spider to use these tools instead of attacking.

Switching between configurations takes 1 action, as legs sprout into its spider-turret form, or pull in into the classic crossbow configuration.

Finally, regardless of configuration, if the Witchbane's Eye is used to attack an Evil aligned Mage it deals an additional 1d4 Psychic Damage to that target. 

Proficiency with a Hand Crossbow allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Damage: Psychic, Bonus: Magic, Damage: Force, Damage: Psychic, Blinded, by a Fighter, Rogue, Ranger or Artificer. You must spend a day fiddling with the mechanical creature, understanding its inner workings and learning to command and control it, binding it to your will., Damage, Combat, Sentient, divination, Ammunition, Light, Loading, Range, Vex