At first glance this blade appears to only be a hilt of black onyx and obsidian. With the mental command of its wielder the sword will ignite into a brilliant and bright energy that leaks dark smoke. While the blade exists, this magic longsword has the finesse property. If you are proficient with shortswords or longswords, you are proficient with the Voidblade.

A Voidblade is a +1 longsword that deals force damage in place of its normal slashing damage. Additionally the sword has 4 charges and replenishes 1d4 charges at dawn. Once you have damaged an enemy with the blade, you can choose to expend a charge. the target must make a Constitution saving throw. if they fail you can pick one of the following effects to take effect on them. An enemy can only have a single negative effect from this blade on them at a time. Rolling a critical hit replenishes one charge to the blade

the DC for this blade is equal to 8+Proficiency bonus+Strength modifier

• the creature loses the ability to regain hitpoints until the end of your next turn.
• the target creature becomes blind until the end of your next turn.
• the target cannot cast spells that affect others until the end of its next turn.
• you siphon the damage inflicted on the target healing yourself the amount of force damage dealt

limited memory

the Voidblade contains memories of its previous wielders and has a limited sentience. if someone attuned to the weapon achieves something of note (at the dms discretion) then the weapon can awaken from its slumbering state.

Awakened 

The voidblade becomes a +2 longsword and the amount of maximum charges increases to 6, and you the amount you regain at dawn increases to 1d4+2. additionally as an action, you can choose to expend three charges to cast the shadow of moil spell on you once per day. It maintains concentration on it so that you don’t have to.

Bonded

When the voidblade chooses to bond with a wielder, they--and they alone--no longer require attunement to wield it to its full capacity. Also, the voidblade becomes a +3 longsword and the amount of maximum charges increases to 9, and you the amount you regain at dawn increases to 1d6+3 Additionally, while wielding this blade it deals 1d8 additional force damage when you hit with an attack using the weapon.

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

Notes: Bonus: Magic, Damage: Force, Blinded, Versatile, Sap