The Dimensional Blade (5e Equipment)
From D&D Wiki
Weapon (Longsword), artifact (Requires attunement)
This ordinary looking sword has a special blade that displaces material that it makes contact with and places it into a small plane of existence held within inside of the sharp edge of the blade. The amount of displaced material is effectively the surface area of the edge. This makes it seem as if the sword can cut through anything, even incorporeal beings. The blade is activated when the handle is held in direct contact of it’s Attuned wielder. When the sword is not active is functions like a normal non-magic longsword This sword when activated however is very dangerous, The wielder must block direct contact with their hand in order to sheath or stow it, ei: gloves. Critical failures can also mean losing an arm or leg, so beware! Due to it's appearance its also quite possible adventurers have found this sword without even know it. Detect magic will faintly show traces of magic if the sword is not active. This is the only way to truly discern this sword from an ordinary one besides this, the sword is seemingly unbreakable. Additionally no visual effects can be seen when the sword is activated.
Lore: Nobody knows who made the sword, it’s magical power has never been understood. Most of the accounts of it have only been heard in children’s tales. However some do believe it is hidden out there in the world as its evidence of destructive power has been witnessed in brief pockets of history.Though the sword appears to have many names, it is always depicted to be quite an ordinary sword. People of all races and backgrounds have previously held the sword in many of these stories. Scholars have remained skeptical of its existence, as it may have well served as some kind of symbolism among the countless stories and folklore around the world. Overtime records began to vanish, and so would the existence of the unknown sword itself, could it be possible that these stories are true?
With its power attacking a creature allows you to cut off a single limb by removing the connected material. If the creature can survive without its limbs or head it may continue to fight, if this is not the case the victim will die. A limb is cut off whenever you roll equal to a targets AC, however if you roll 3 or above past the enemies AC you instead strike a vital area, killing the enemy instantly at the DM’s discretion. You cannot instantly kill creatures any bigger than Large, and cutting limbs take 1 extra strike per size level above medium for creatures above large. If you ever get a critical hit, you instantly kill the enemy by striking a vital spot no matter the size of the creature, Creatures with legendary resistance can automatically survive a critical hit or vital strike at the cost of one of their saving throws. When this is the case a limb is instantly cut instead of making a vital strike regardless of size. Weapons, Shields, items and structures can also be cut when attacked. Targets wielding a shield have them cut in two when successfully attacked, destroying it, and parrying attacks with the weapon, cuts the opponent's weapon. Magic weapons and items can also be cut, but in some cases they may remain functional. Wards, barriers, portals and other forms of magic can also be cut by the sword.
Destroying the The Dimensional Blade. Only a wish spell can destroy the sword