The Yklwa can be found in Tomb of Annihilation, page 32.
This magic weapon has a dull, rusty color or has veins of ruidium running through it. While this weapon is on your person, you gain the following benefits:
A creature you hit with this weapon takes an extra 2d6 psychic damage.
When you roll a 1 on an attack roll made with this weapon, you must make a DC 20 Charisma saving throw. On a failed save, you gain 1 level of exhaustion. If you are not already suffering from ruidium corruption, you become corrupted when you fail this save.
If the Apotheon is killed or redeemed, all the ruidium in Exandria is destroyed instantly, and a ruidium weapon becomes a +2 weapon.
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.