Weapon

Legendary Requires Attunement

You gain a +1 bonus to attack and damage rolls made with this greatsword. As a bonus action, you can speak a command word, causing flames to erupt from the blade. These flames shed bright light in a 20-foot radius and dim light for an additional 20 feet. While the greatsword is ablaze, it deals an additional 1d6 fire damage on hit. The flames last until you use a bonus action to speak the command word again or until you drop or sheathe the greatsword.  

Awakened

When a character awakens this item, apply the following changes to the item's traits.

You gain a +2 bonus to attack and damage rolls made with this great sword.

The fire damage dealt increases to 2d6.

When you make an attack while the greatsword is ablaze and roll a natural 20, a Fireball (level 3, DC14) centered on your target explodes. The Fireball blossoms out in a 20-foot radius damaging everyone in the blast, excluding yourself. The fireball spreads around corners and ignites flammable objects in the area that aren't being worn or carried.

Exalted

When a character exalts this item, apply the following changes to the item's traits.

You gain a +3 bonus to attack and damage rolls made with this great sword.

If you drop to 0 hit points while the greatsword is ablaze, you can make a DC 10 Constitution saving throw. If you succeed, you drop to 1 hit point instead. Each time you use this feature the DC increases by 8. When you finish a long rest the DC resets to 10.