The Double-Bladed Scimitar can be found in Eberron: Rising from the Last War, page 21.
You gain a +3 bonus to attack and damage rolls made with this sword. Hit points lost to this weapon's damage can be regained only through a short or long rest, rather than by regeneration, magic, or any other means.
You're unwilling to part with this weapon while attuned to it. While attuned to this weapon, you also have disadvantage on attack rolls made with weapons other than this one.
The vengeful spirit possessing the sword shares its history and lust for vengeance with the wielder. After each successful long rest, you experience nightmares of the spirit's past, culminating in its death. When you wake, you must make a DC 11 Constitution saving throw. On a failed save, you only gain the benefits of a short rest. Only the Remove Curse spell allows you to end attunement to this item.
This item corrupts. See the "Infernal Item Corruption" section.
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.
This weapon requires two hands to use. This property is relevant only when you attack with the weapon, not when you simply hold it.