Based on a manga story from Ranma ½ volume 34.

http://www.furinkan.com/features/art...umicworld.html

Twelve years after the final OVA was shown, and the end of the manga, a new piece of Ranma ½ animation was made for the "It's a Rumic World" exhibition of Rumiko Takahashi's artwork. The new 30 minute special is based on the "Nightmare! Incense of Spring Sleep" manga story from volume 34, and was shown on odd numbered days at the "It's A Rumic World" exhibition in Tokyo from July 30th to August 11th. together with two other specials for Urusei Yatsura and Ranma 1/2.
source: wikipedia

On January 29, 2010 a limited edition “It’s a Rumic World Special Anime Box” DVD collection was released which contains all three specials.
As you can guess from my nickname, I was pleasently surprised when I recently found this OAV subbed. Its been 2 years since it was shown in Japan in the Rumic World Exhibition and it was finally released on DVD a few months ago.

As a Ranma fan it brough a tremendous grin to my face through all the episode. Specially since we got to see many characters that weren't shown or didn't had enough screentime on the animated series.

Unlimited Translation Works Ranma Deep Sleep Incense OAV