The Yklwa can be found in Tomb of Annihilation, page 32.
You gain a +3 bonus to attack rolls and damage rolls made with this magic weapon. When you hit a Fiend or an Undead with it, that creature takes an extra 2d10 Radiant damage.
While you hold the drawn weapon, it creates a 10-foot Emanation [Area of Effect] originating from you. You and all creatures Friendly [Attitude] to you in the Emanation [Area of Effect] have Advantage on saving throws against spells and other magical effects. If you have 17 or more levels in the Paladin class, the size of the Emanation [Area of Effect] increases to 30 feet.
A yklwa (pronounced YICK-ul-wah) is a simple melee weapon that is the traditional weapon of Chultan warriors. A yklwa consists of a 3-foot wooden shaft with a steel or stone blade up to 18 inches long. Although it has the thrown weapon property, the yklwa is not well balanced for throwing.
If a weapon has the thrown property, you can throw the weapon to make a ranged attack. If the weapon is a melee weapon, you use the same ability modifier for that attack roll and damage roll that you would use for a melee attack with the weapon. For example, if you throw a handaxe, you use your Strength, but if you throw a dagger, you can use either your Strength or your Dexterity, since the dagger has the finesse property.