The Dragones Potion was a potion created by the Dragon Priests, that consisted of Urgash's blood, infused with magic. It was an alternate way of defeating Urgash if a Dragon Emperor wasn't present or capable to defeat him. Since it was incredibly hard to make, only high ranking dragons had access to it. It was used to weaken him to the strength of a normal dragon and imprison him (since he was immortal, he could not be killed only imprisoned).