"Nightmare Hakusho" is a neat bonus OVA for fans of the series. It features four different dreams that Yuusuke experiences, all featuring the rest of the main cast wildly out of character, in bizarre scenarios. Genkai is a confused, timid elevator operator and Hiei is friendly and smiles at something other than the prospect of killing a foe.
It's not hysterically funny nor tremendously creative and picturesque, but it's amusing enough, and doesn't wear out its welcome at a mere 8 minutes long.
Fans of YYH and its iconic characters will enjoy this, as I did, but don't expect anything remotely as good or memorable as the main show.