The Yklwa can be found in Tomb of Annihilation, page 32.
You gain a +1 bonus to attack rolls and damage rolls made with this magic weapon.
When you hit a Giant with this weapon, the Giant takes an extra 2d6 damage of the weapon's type and must succeed on a DC 15 Strength saving throw or have the Prone condition.
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.