Very Rare Weapon (Longsword), Versatile, Requires Attunement

• You gain +1 bonus to attack and damage rolls made with this magical weapon 
• Deals extra 1d10 force damage to Aberrations, Constructs, Fiends and Undead 

Destroyer of Unnatural. If you bring an Aberration, Construct, Fiend or Undead to 0 HP, you can use your reaction to disintegrate them, as via the Disintegration spell, and heal yourself and any allied creature within 30 feet for 2d10 hit points. 
Natural Disaster. Once per long rest, you can cast one of the following spells (DC 13) using the weapon. Erupting Earth, Fireball, Sleet Storm, Tidal Wave, Thunder Step.
Aberrations, Constructs, Fiends and Undead have disadvantage on saving throws imposed by these spells when cast through the weapon.
This weapon can also be used exactly once to cast Earthquake (DC 18), but doing so will permanently remove the ability to cast spells through the item.