Weapon (rapier), rare
This short, steel, straight-bladed rapier reflects light, but it never shines. Its metal remains a pale metallic grey no matter how diligently cleaned and polished, as if forged from an ingot of heavy fog. Its basket hilt has a cloud motif, hiding the wielder's hand in a roiling fog and making it harder to predict where the blade will move next.
The wielder gains a +1 bonus to attack and damage rolls with this weapon. When the wielder wishes, the Mist Rapier glows with a purple faerie fire effect, radiating dim light in a 10 foot radius.
When readied for combat, the Mist Rapier makes a small (3 foot diameter) fog cloud around the blade, not enough for the wielder to hide in, but enough to gain advantage on the first attack roll made with it. Opponents see several purple glowing blades thrusting out of the mist for the first attack, but only one of them (the non-illusion) will do damage. The movement of the initial attack will dissipate the cloud into fog tendrils and leave the blade visible.
On subsequent rounds of combat, the Mist Rapier can generate a new fog cloud, but only if the user moves no more than 30 feet and refrains from attacking in the round immediately prior. Normal combat use and fast movement dissipates the fog faster than the rapier can create it. Anything stronger than a light wind will also prevent the fog from gathering, as from a gust of wind spell or even a gust cantrip.
Mel Brattle, the Forest Gnome duelist and proprietor of The Happy Bowl ramen bar, wields a Mist Rapier as his primary weapon. On calm days he uses the blade's fog effect to enhance his performance when attracting customers, usually after his dagger juggling routine grows a little stale.