Ghost Cutlass

Weapon (scimitar), uncommon
  As a bonus action you can speak this round, rusted hilt’s command word. A curved blade of ethereal green smoke sprouts from the barnacle-encrusted metal and swims with ghastly, ghostly visages. Legend says these faces belong to those who fell whilst wielding the blade, a part of their soul trapped forever in its decrepit metal.
  You have a +1 bonus to attack and damage rolls made with this magic weapon, which deals psychic damage instead of slashing damage.
  Hydrodynamic. Attacking while underwater doesn’t impose disadvantage on attack rolls you make with this weapon.
  Rare variant: Increase the bonus to + 2.
  Very rare variant: Increase the bonus to + 3