A double bladed scimitar which does 2d6 damage 

When attuned you can deal and additional 2d4 (?) damage after expending a spell slot into the sword.

After expending the spell slot as a bonus action, roll a d4 for damage type to apply

Once activated with damage type the blades begin to glow and take form as a searing beam of the determined damage type. (Like a lightsaber)

1-Radiant

2-Lightning

3-Fire

4-Cold

The double-bladed scimitar is the signature weapon of Valenar elves. A haft of fine wood supports a long, curving blade on either end. Forged with techniques honed over centuries, these blades are strong, sharp, and remarkably light. Each scimitar is a masterpiece, and as a result the double-bladed scimitar is an expensive weapon (100 gp) — few though ever have the opportunity to purchase one. A Valenar blade in the hands of a non-elf is generally assumed to have been stolen or looted from a fallen foe, and a Valenar elf might feel entitled to demand its return or challenge the bearer to prove they’re worthy to wield it.

Special. If you attack with a double-bladed scimitar as part of the Attack action on your turn, you can use a bonus action immediately after to make a melee attack with it. This attack deals 1d4 slashing damage on a hit, instead of 2d4.

Notes: Damage: Lightning, When attuned the user can empower the weapon and alter it's capabilities., Special, Two-Handed