Crescent of Ash, Naginata of the Ashen Veil

Forged by the blade smiths of the Ashen Veil, this polearm is a masterpiece of balance between elegance and destruction. Its curved, single-edged blade flows seamlessly into a shaft of lacquered blackwood reinforced with folded steel, the metal’s Damascus pattern rippling like water frozen mid-motion. Each weapon bears the mark of its maker: Gilded fittings, engraved guards, and hanging cords of silk or leather. All symbols of the bearer’s command over both artistry and war.

You have a +3 bonus to attack and damage rolls made with this magic weapon.

This weapon has the finesse and reach properties.

When you make an attack of opportunity, you can make two attacks instead of one.

You can choose to attune to this weapon. While attuned, you gain the following benefit:
Elemental Armament.
The polearm deals an additional 2d8 damage of a type of your choice: acid, cold, fire, force, lightning, necrotic, poison, psychic, radiant, or thunder. You choose the damage type when you finish a long rest, and you can change it whenever you finish another long rest.

As a bonus action, you can prematurely change the polearm's elemental damage type to another option from the list above.

Elemental Flow.
When you take the Attack action, you can forgo your other attacks to make a single sweeping strike imbued with the naginata’s elemental power. All creatures of your choice within your reach must make a Dexterity saving throw (DC = 8 + your proficiency bonus + your Strength or Dexterity modifier). On a failed save, a creature takes 5d10 damage of the polearm's current elemental type. On a successful save, it takes half as much damage.

You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Spire of the Element.
As an action, you drive the polearm into the ground, releasing the elemental essence bound within its steel. The terrain within a 20-foot radius centered on you twists and reshapes into a manifestation of your chosen element for one minute. The ground becomes difficult terrain for all creatures other than you as the air hums and shimmers with unstable energy.

While the Spire of the Element remains active, any creature that enters the affected area for the first time on a turn or begins its turn there is seared, frozen, or otherwise scorched by elemental force, taking 2d10 damage of the polearm's current elemental type.

On your turn, you can use a bonus action to command the terrain to surge violently in response to your will. When you do so, all creature within the area must succeed on a Strength saving throw (DC = 8 + your proficiency bonus + your Strength or Dexterity modifier) or be knocked prone and take 2d10 damage of the polearm's elemental type.

Once you use this feature, you can’t use it again until you finish a long rest.

Proficiency with a Glaive allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Weapon Property: Finesse, Damage: Acid, Damage, Combat, Heavy, Reach, Two-Handed, Graze