Quote from PenelopeTheWeaver >>

I wasn’t familiar with the Valenar.

 They were in WGtE (pre E:RftLW) and didn’t make it to the final publication, but their weapon (and feat) did:

Double-Bladed Scimitar

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.

A double-bladed scimitar is a martial weapon, weighing 6 pounds and dealing 2d4 slashing damage on a hit. It has the two-handed property and the following special property:

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.

Feat: Revenant Blade

Prerequisite: Elf

You are descended from a master of the double-bladed scimitar, and some of that mastery has passed on to you. You gain the following benefits:

• Increase your Dexterity or Strength score by 1, to a maximum of 20.
• While you are holding a double-bladed scimitar with two hands, you gain a +1 bonus to Armor Class.
• A double-bladed scimitar has the finesse property when you wield it.

Cool. I read the 5e Eberron book but I don’t remember seeing them.

Quote from PenelopeTheWeaver >>

Cool. I read the 5e Eberron book but I don’t remember seeing them.

 Under the Elf entry in the race section. Like I said, “Valenar elves” didn’t make it through playtesting into the final book, so they only appeared in WGtE (the live document dumpster fire that came out before Eberron: Rising) but the weapon and the feat as well as the name “Valenar” are in Eberron: Rising.

@IAmSposta thanks.