Amulet of Severed Smoke

This fist-sized metal disk periodically emits black smoke from its sides. The smoke forms into the shape of a longsword before dissipating.

This magic item has 3 charges. While holding it, you may expend any number of charges, to cast the spell fog cloud at a level equal to the number of charges spent this way. All charges restore at dawn. Instead of fog, the spell produces a thick black smoke. In addition, whenever a creature moves into the spells area for the first time in a turn or starts its turn there, make a melee spell attack roll against that creature (+5 to hit). On a hit, the target takes 2d8 slashing damage as a sword forms out of the smoke and attacks them.