The Yklwa of Warning is a magical item that can be found in the Tomb of Annihilation. It has the ability to warn you of danger. If you have it on your person, it has the power to give you the advantage whenever you have to roll for initiative. It also has the power to make you and any of your companions in a range of 30 feet immune to surprise. The rest of the stats are equal to the regular Yklwa. It is a pretty cool weapon, which you can read more about in the DMG book on page 213.