Banisher

The Banisher is a mighty weapon only wielded by the strongest of warriors, designed to banish powerful foes from the realms, or at the very least... slaughter them where they stand. This weapon counts as a +3 longsword. While attuned to it you gain immunity to acid damage, and have advantage on saves that try to resist any form of banishment or forced teleportation.

Banishment - When you hit a creature with this weapon, you may use a bonus action to try and banish them. The creature must succeed on a DC 26 charisma saving throw or be banished from the current realm, sending them into the realm of the very first Banisher blade completely engulfed in flames. A creature who fails but is not banished instead takes 23 (5d8) force damage. While in this realm, creatures take 45 (10d8) fire damage at the start of their turn, and are unable to gain any long rest benefits. You can use this ability an amount of times equal to your proficiency bonus, and resets on a long rest.

Pursuit - At the start of your turn you may have a small portal open up near one creature within 120ft of you. You are considered to be in melee with the creature, and if you hit the creature with this blade, it latches onto the target and teleports you within 5ft of them. The portal only holds up enough for the attacker to get one chance, after the first attack it closes, regardless on whether you hit or not.

Slaughter - Sometimes foes are to powerful to be banished, and must therefore be felled where they stand. While attuned to this weapon your crit range increases by two, and the weapon deals an additional 13 (2d12) acid damage. Whenever you score a critical hit on a creature, they must make a constitution save equal to half the total damage or have their AC reduced by one. 

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, Immunity: Acid, Damage: Acid, creature who has felled the previous wielder, Versatile, Sap