- Talk to Esbern or Delphine.
- Kill Paarthurnax
This quest is given to you if during Season Unending, you talk to Esbern. Delphine and Esbern have discovered that Paarthurnax is the Master of the Greybeards. Esbern will tell you that Paarthurnax is an ancient enemy of the Blades, and insist that you kill him.
Paarthurnax will be at the The Throat of the World. If you talk to him after the conversation with Esbern, he acknowledges that all dragons thirst for power, though he believes that he has overcome this in-built nature through sheer willpower and that he can be trusted.
If you talk to Arngeir and tell him that the Blades want Paarthurnax dead, he will tell you that – although what Esbern said is true – it was because all dragons were in league with Alduin at first, and that Paarthurnax could not help it. He will go on to say that Paarthurnax did eventually rebel against Alduin, and was instrumental in Alduin’s first demise. You are given the option to tell him Paarthurnax must die or that you are going to spare him. This will affect the conversation between Esbern and Arngeir if in Season Unending you are forced to negotiate a treaty.
Paarthurnax is an easy foe for those who are leveled sufficiently, comparable to the average Frost dragon. You will receive a Dragon Soul and the usual set of bones and scales upon defeating him.
Killing Paarthurnax will enrage Arngeir who, if you return to High Hrothgar, will angrily lecture you on your decision and even go so far as to threaten violence if you do not leave. After this, the other Greybeards will also fail to acknowledge you. On the other hand, the Blades will talk to you again, and you can sell Esbern any Dragon Bones and Dragon Scales you take to him.
If you let Paarthurnax live, there will be a short scene with him after you have defeated Alduin for good, and he will tell you that he will try to round up the other dragons and bring them into the Way of the Voice, teaching them how to be peaceful.