There is very little known about the artificer that made this magical sheath but it is thought that he was incredibly exccentric and paranoid about his creations being stolen.

When unattuned this item is a regular scabbard made to hold a shortsword

When attuned the Scabbard of Intangibility displays two abilities, Perfect Sheath and Intangable Strikes.

Perfect Sheath:

The user may place any of the following weapons at the mouth of the scabbard and place it inside:

1. a longsword
2. a shortsword
3. a rapier
4. a greatsword
5. a scimitar

Once a weapon is placed inside the scabbard the appearance changes to match a scabbard of the same type as the weapon inside and will stay that way until a weapon of a different type is stored.

Intangible Strikes:

As a bonus action the user places their weapon into the scabbard and twists the handle giving the sheathed weapon the ability to interact directly with intangible creatures and objects. This allows the weapon to bypass the damage resistances of intangible creatures allowing the weapon to do full damage instead.

The inherently ethereal nature of the weapon inside the scabbard of intangibility results in the weapon's damage being reduced by one die type to a minimum of a d4. for example a non magical rapier does 1d8 damage, if it was within the scabbard of intangibility it would do 1d6 damage. Additionally while the weapon is within the scabbard it cannot harm corporeal creatures and objects, passing right through them.

When this weapon strikes an invulnerable intangible object such as the sensor produced by the  clairvoyance spell it instead moves the object a distance given by half the damage roll of the weapon in feet.

As a bonus action the user places the handgard of their weapon to the mouth of the scabbard and twists the handle again resulting in the weapon returning to a tangible state, undoing the effects of the Intangible Strikes feature.