Scythe of the Headless Seahorseman

Weapon (glaive or halberd), rare (requires attunement)
  This rusted scythe, with its driftwood handle that supports a plethora of sea life, is surprisingly light and hydrodynamic. Attacking while underwater doesn’t impose disadvantage on attack rolls you make with this weapon.
  Fearflame. As a bonus action you can speak the weapon’s command word causing an eerie green flame to shimmer along the blade’s length. For the duration, whenever you hit with this magical weapon, the target takes an additional 1d6 psychic damage and must succeed on a DC 15 Wisdom saving throw or become frightened of you until the start of your next turn. If you roll a 6 for the psychic damage, the green flame disappears ending the effect, and you can’t use this property again until the following dawn.
  Phantom Steed. As an action you can speak the scythe’s second command word and cast the phantom steed spell. The creature always appears as an amphibian seamare. This takes the statistics of a giant sea horse with the following changes:
  • It has a walking and swim speed of 100 feet.
  • It has the ‘Amphibious’ trait instead of the ‘Water Breathing’ trait.
  • It has the Frightful Presence action (DC 15 Wisdom saving throw, 60-foot radius).
  Once you use the Phantom Steed feature, you can’t do so again until the following dawn.
  Hydrodynamic. Attacking while underwater doesn’t impose disadvantage on attack rolls you make with this weapon.
  Very rare variant: Increase the damage to 1d8 psychic damage, and the DC to 16.
  Legendary variant: Increase the damage to 2d6 psychic damage, and the DC to 17. Phantom steed can be cast as an action at will, but you can only have one steed present at once.