Dragonbane is a +3 longsword with all the properties of a dragonslayer, holy avenger, permanent arrow of chromatic dragon slaying, and vorpal sword. All damage abilities are stacked.  Dragonbane has a dragon skull on the cross guard and the hilt is very long, even for a bastard sword. Also, the blade is made of an unknown white metal. Dragonbane speaks in a deep male voice but prefers to stay quiet most of the time. This changes once a dragon is encountered. Dragonbane will fully illuminate and begin swearing and taunting the dragon in Draconic. It is impossible to surprise a dragon with Dragonbane.

Dragonbane has the following statistics: Int 16 Wis 18 Cha 18. Lawful Good. Hearing and darkvision to 120 ft. Speaks Common and Draconic and communicates telepathically with its wielder. Once Dragonbane tastes dragon’s blood, there will be conflict if the wielder decides to run or stop fighting before the dragon is dead. Dragonbane also prefers to be wielded with two hands.

The first time the wielder attunes Dragonbane, the wielder must go kill a dragon as if affected by the geas spell. Once this quest is completed, the wielder is no longer affected by it. While attuned to Dragonbane the wielder cannot be charmed or frightened and has resistance against dragon breath weapons. Strength increases by +2 to a maximum of 24. Chromatic dragons are always hostile to the wielder.

It is said that Dragonbane can be destroyed if plunged into the heart of a platinum dragon.

You gain a +3 bonus to attack and damage rolls made with this magic weapon. When you hit a fiend or an undead with it, that creature takes an extra 2d10 radiant damage.

While you hold the drawn sword, it creates an aura in a 10-foot radius around you. You and all creatures friendly to you in the aura have advantage on saving throws against spells and other magical effects. If you have 17 or more levels in the paladin class, the radius of the aura increases to 30 feet.

When you hit a dragon with this weapon, the dragon takes an extra 3d6 points of slashing damage. For the purpose of this weapon, "dragon" refers to any creature with the dragon type, including dragon turtles and wyverns.

If a chromatic dragon takes damage from the sword, the creature must make a DC 17 Constitution saving throw, taking an extra 6d10 slashing damage on a failed save, or half as much extra damage on a successful one.

The weapon ignores resistance to slashing damage.

When you attack a creature that has at least one head with this weapon and roll a 20 on the attack roll, you cut off one of the creature's heads. The creature dies if it can't survive without the lost head. A creature is immune to this effect if it is immune to slashing damage, doesn't have or need a head, has legendary actions, or the GM decides that the creature is too big for its head to be cut off with this weapon. Such a creature instead takes an extra 6d8 slashing damage from the hit.

 

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

Notes: Bonus: Magic, Damage: Radiant, Advantage: Saving Throws, Favored Enemy: Dragons, Damage: Slashing, Immunity: Charmed, Immunity: Frightened, Damage: Slashing, Bonus: Ability Score Maximum, Bonus: Strength Score, Version 2.2 fixed the problem with adding 2 points to Strength. It wasn't adding it on the character sheet when attuned., Paladin, Damage, Combat, Sentient, Versatile