It is time to fulfill your destiny Dragonborn. With your allies by your side, destroy the dragon god Aludin World-Eater and save the land of Skyrim and the souls of its dead from his evil.
Leave the Hall of Valor and make your way across the whale skeleton bridge and over to the edge of the Shadowed Vale, where your three Nordic allies are gathered. When you’re all together, use your Clear Skies shout to dispel Alduin’s protective mist – the other three will add their voices to yours. Alduin bellows back with a shout of his own, causing the mist to descend once again. Continue shouting together with your allies and eventually the mist will vanish entirely.
With his cloak dispelled, Alduin will swoop down in the vale and begin spewing fire at you, your allies, and any of the lost souls that were caught in the mist. It is imperative you use Dragonrend against him as he is completely invulnerable until you do. When he’s been brought down to the ground, move in to attack him together with your allies. Alduin will have to divide his attention between all of you, while each of you only have to worry about attacking him. When your Dragon Shout meter regenerates, if he’s still on the ground from the effects of Dragonrend, use another shout against him (Fire Breath works well). Apart from that, just attack as you normally would with your favored weapons or magic spells. Just remember that if he recovers from Dragonrend you’ll have to use it on him again before you can continue your attack.
After one of you strikes the fatal blow, Alduin writhes in agony as his soul departs his corporeal form and dissipates, until with a final, thunderous spasm, he is entirely torn apart, leaving not a skeleton or any other physical remains in this afterlife. Tsun is the first to congratulate you for what you have done. You can speak to any of your allies again, but when you’re ready to return to the mortal world, talk to Tsun again and he’ll transport you to back to Skyrim. Before he does, however, he teaches you a Dragon Shout that summons a hero from Sovngarde to aid you in battle if you should find yourself in need.
You return to the Throat of the World, where a retinue of dragons are perched on the mountaintop and roaring a death chant for their fallen god – their leader, Alduin. When they’re done and they fly off, two recognizable dragons remain: Paarthurnax and Odahviing. Paarthurnax greets you, impressed at what you have done, before flying away after the others, leaving only Odahviing, who informs you that he is now in your service. From this point on you can shout his name to summon him to your side in battle.
NOTE: If you killed Paarthurnax at the request of the Blades, then needless to say he won’t be on the mountaintop with the other dragons waiting to congratulate you.
Return to High Hrothgar and speak with Master Arngeir. Inform him of your actions. He believes that Alduin may yet rise again, but that is for the gods to decide.
If you return to Sky Haven Temple and tell the Blades what you have done, they’ll be happy and grateful, but they’ll still be the matter of Alduin’s brother Paarthurnax, who in their mind should pay for his past crimes with his life.
The land of Skyrim has been saved from the great evil that threatened it. You can now explore it at your leisure for the rest of your life.