I searched this on wikipedia and i found this:
http://en.wikipedia.org/wiki/List_of_YuYu_Hakusho_episodesThat has all the episodes with a great description. This is where u were up to i think: In the Chapter Black Saga, Yusuke must stop Shinobu Sensui from opening a gate to demon world while defeating six other humans with newly awakened psychic powers. When he realizes he cannot defeat Sensui's true self, he decides to have Sensui kill him to awake Hiei, Kurama, and Kuwabara's hidden potential. After he dies, his ancestral demonic blood resurrects him. It is revealed that he is a Mazoku, or a descendant of a Yōkai Clan (the Amazaku demons in the English anime), his ancestor Raizen having conceived a child with a human woman. Raizen made it so that when the stars reach a certain alignment, and his descendant is worthy of awakening, they would become a yōkai. It was Yusuke's first death that awoke his potential, and awoke his hidden reiki powers. It was his subsequent missions afterwards, especially his fight against the younger Toguro, that helped begin to awaken his dormant yōkai blood. However, in the end, it was his death at the hands of Sensui that pushed his change over the edge and completely changed him, allowing demonic kinship symbols to emerge all over his body. After this transformation, he fights Sensui on even footing until he is then possessed by his anscestor Raizen to help control his new-found power and as a result Raizen, through Yusuke's body, kills Sensui which upsets Yusuke greatly.
After that is the final saga The Three Kings Saga. So you can scrool down to that.