A Needle Sickly
This magic weapon is the product of precise tinkering with poisons and other corrosive materials by an Artificer. It combines magical infusions with mechanical delivery mechanisms to unleash its harmful effects - sometimes with the press of a button, sometimes through mere thought. As a result of this entanglement between weapon and mind, it requires both attunement and infusion by the artificer who created it.

Crafting the weapon: To create this weapon, an Artificer has to infuse a melee weapon with any applicable infusion. The weapon keeps any effects granted by the infusion. They then must spend a day working on the weapon, and in the process expend a vial of basic poison and a vial of acid to infuse their effects into the weapon in the form of charges. At creation, this weapon has 1 maximum charge. Spending 1 vial of basic poison (or any other poison or acid worth 100 gold) and 1 hour of time, the artificer can add an additional maximum charge to this weapon. The cost of adding further charges increases by 1 vial after every even charge added, so charge 3 costs 2 vials, charge 5 costs 3 vials, etc.

Mechanics:
Charges: This weapon uses charges that must be expended to use its effects. It regains all charges at the end of a long rest.
Damage Infusion: This weapon can deal additional poison, acid, or necrotic damage. You can choose the damage type whenever you activate one of these damaging effects. This damage increases with the wielder's Proficiency Bonus: 1d4 at PB 2, 2d4 at PB 3, 3d4 at PB 4, 4d4 at PB 5, and 5d4 at PB 6.
Saving Throw DC: If any weapon effect requires a saving throw, the DC for that saving throw is equal to 8 + PB + INT modifier of the weapon wielder.

Effects:
Sickly Strike: Once per turn when hitting a target with this weapon, you can spend 1 charge to inject the target with poison, acid, or a necrotic mixture of both, dealing additional damage of the chosen type according to the current Damage Infusion. When using this option, you can not activate any of the other additional effects on this attack.
Sickly Ooze: As a bonus action, you can press a hidden button on the hilt to spend 1 charge to coat this weapon with poison, acid, or a necrotic mixture of both. For 1 minute, this weapon deals additional damage of that type according to the current Damage Infusion. You can deal this extra damage once per turn.
Sickly Calamity: As an action, you can press the hidden button to spend 1 charge to unleash poison, acid, or a necrotic mixture of both in a cone with a size of 10 times your PB feet. Each creature in that area must make a Dexterity saving throw, taking damage according to the current Damage Infusion times your PB on a failed save, or half as much damage on a successful one. Once this action is used, you can't use it again until you finish a long rest.

Additional effects:
When hitting a target with this weapon, you can expend the specified number of d4s to inflict an additional effect. You do this by expending enough charges so that your Damage Infusion covers the cost of the effect, and then deal any excess as damage of the effect type you used. So at PB 3 you could spend 1 charge, equal to 2d4s, to use one of the first three effects. At PB 5, you could spend 3 charges, equal to 12d4, to use one of the last three effects, and deal the excess 2d4 as damage. On a critical hit, the target has disadvantage on the initial saving throw. The first 3 effects unlock at PB 3, the next 3 at PB 4, and the last 3 at PB 5. You can choose up to 3 unlocked effects to be prepared for use, and can switch that selection whenever you finish a long rest. Only 1 option can be activated per attack.

Noxious Poison: You can spend 2d4 to force the target to make a Constitution saving throw. On a failed save, the target has the Poisoned condition for 1 minute. At the end of each of its turns, the poisoned target repeats the save, ending the effect on itself on a success.
Stripping Acid: You can spend 2d4 to force the target to make a Dexterity saving throw. On a failed save, the target has its AC reduced by 2 for 1 minute.
Necrotic Touch: You can spend 2d4 to force the target to make a Constitution saving throw. On a failed save, the target can't regain hitpoints until the start of you next turn and you gain 2d4 temporary hitpoints.
Blinding Poison: You can spend 6d4 to force the target to make a Dexterity saving throw. On a failed save, the target is blinded until the start of your next turn.
Corrosive Acid: You can spend 6d4 to force the target to make a Constitution saving throw. On a failed save, the target gains Vulnerability to bludgeoning, piercing, and slashing damage until the start of your next turn.
Necrotic Drain: You can spend 6d4 to force the target to make a Constitution saving throw. On a failed save, you heal by 6d4, or half as much on a successful save. On a critical hit, the healing dice double.
Stupefying Poison: You can spend 10d4 to force the target to make an Intelligence saving throw. On a failed save, the target is confused for 1 minute. Whenever the target makes an attack roll, it has to roll a D20. On a 11 or higher, it can attack as normal, on a 10 or lower, it targets itself instead. At the end of each of its turns, the confused target repeats the save, ending the effect on itself on a success.
Burning Acid: You can spend 10d4 to force the target to make a Dexterity saving throw. On a failed save, an object worn or carried by the target is splattered with acid, distracting the target. As long as it wears or carries this object, it has disadvantage on attack rolls, skill checks and saving throws, and attack rolls against the creature have advantage. The acid can be removed by spending an action to clean the object.
Necrotic Fatigue: You can spend 10d4 to force the target to make a Constitution saving throw. On a failed save, the target receives 2 levels of exhaustion. At the end of each of its turns, it repeats this saving throw, receiving another level of exhaustion on a fail. On a success, it can stop making further saving throws, but already accumulated exhaustion levels remain for 1 minute. While it has these exhaustion levels, the target can't be affected by additional instances of Necrotic Fatigue, and for every of these exhaustion levels affecting it, you gain a buff corresponding to the exhaustion effect. In order of the exhaustion levels, these buffs are: You have advantage on skills checks; Your movement speed is doubled; You have advantage on attack rolls and saving throws; Your hit point maximum is doubled; You can use action surge once per turn. Finally, if the target dies to exhaustion, you gain all previous buffs for 1 minute, and this weapon regains all expended charges. If the target doesn't die to exhaustion, but while still being affected by any level of exhaustion caused by Necrotic Fatigue, you heal by an amount equal to the targets maximum hit points instead.

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

Notes: by an Artificer, Finesse, Vex