Twinblades are martial, bladed melee weapons consisting of polearms with a large blade on each end that deal 2d4 slashing damage on a hit and have the Finesse, Special and Two-Handed properties.

Properties

Finesse
When making an attack with a finesse weapon, you use your choice of your Strength or Dexterity modifier for the attack and damage rolls. You must use the same modifier for both rolls.

Special: Whirl
If you are proficient with the twinblade, you can use a bonus action to attempt to whirl the weapon. Make a DC 15 Dexterity check. On a success, you gain a +2 bonus to your AC until the start of your next turn, the whirling blades acting as a barrier against attacks. On a failure, that bonus is only a +1.

Two-Handed
This weapon requires two hands when you attack with it.

Superior Strike

Whirling Strike.
In a blitzing vortex of aggression, you strike at all those around you in a sinuous assault. Each creature within your reach must make a Dexterity saving throw. A creature takes damage of your weapon’s type equalling a number of d6s equal to your proficiency bonus on a failure, or half as much damage on a success. Success or failure, the creature can’t make opportunity attacks against you until the end of this turn.