Weapon (shortsword), unknown rarity (requires attunement by a must succeed a DC 15 Arcana check, or the Item is curse the player for eternity)
If the player is at level 1, the item can morph from an arm brace to a shortsword (it takes an action to summon)
at level three
Proficiency with a Shortsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.
This weapon has the following mastery property. To use this property, you must have a feature that lets you use it.
Vex. If you hit a creature with this weapon and deal damage to the creature, you have Advantage on your next attack roll against that creature before the end of your next turn.
Notes: must succeed a DC 15 Arcana check, or the Item is curse the player for eternity, Finesse, Light, Vex