The Yklwa can be found in Tomb of Annihilation, page 32.
This weapon is fashioned from infernal iron and traced with veins of hellfire that shed dim light in a 5-foot-radius.
Any humanoid killed by an attack made with this weapon has its soul funneled into the River Styx, where it's reborn instantly as a lemure devil.
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.