"The shadar-kai are an odd lot. Their numbing existence in the Shadowfell has caused many of them to seek extreme experiences just to feel something. Take their favored brew, Umbral Blot, for example. The magically infused booze isn't for lightweights."
Umbral Blot is a strong alcohol made from various shadowfell mushrooms and laced with living shadowstuff. Characters under the affects of Umbral Blot tend to be reckless, gaining disadvantage on Wisdom saving throws. However, the shadowstuff also temporarily transforms their very being, making them more shadow-like. Drinkers gain advantage to stealth ability checks. A strong drink the Constitution saving throw DC to avoid intoxication from Umbral Blot is 20. The effects of Umbral Blot last until the drinker takes a long rest.