- Meet with the heroes of Sovngarde
- Coordinate your shout with theirs to clear Alduin's mist
- Defeat the World-Eater in combat
Leave the Hall of Valor and cross the Whalebone Bridge to the edge of the Shadowed Vale, where your Nordic brethren are gathered. They are eager to slay Alduin just as much as you are. When the three heroes have assembled you will take your place by their side. Once you have done so, one of them will suggest that you all use the "Clear Skies" Shout together to blow away the mist - your companions will wait for you to shout then use their Thu'um as well. You need to do this three times when requested, as Alduin covers the field in mist again the first two times you clear it away. After your third shout, the mist dissipates, Alduin becomes enraged and flies towards you and the final battle is joined.
This is when you begin your last fight with Alduin. Alduin launches a barrage of fire attacks at you, the Nords, and any of the lost souls that have been freed from their permanent fog. Alduin's rain of fire ability hits a large AoE so have wards, healing spells and/or potions ready.
To defeat Alduin, you must once again strike him with Dragonrend to force him to land. Until you do, he is invincible and will take no damage. While on the ground, it is relatively easy to kill him due to the fact that the three Nord heroes will help in the battle. Alduin is basically the same as every other dragon the Dragonborn has thus encountered: melee from the sides to avoid the potent tail attack, have a shield handy if you're planning to go head to head. For archers, Alduin is just as susceptible to potent poisons as other living creatures. Hit from a distance with high damage lingering poisons and he will stay down fairly quickly. For magic users, the "Marked for Death" Shout is very useful as it increases his susceptibility to damage from spells.
After you strike the killing blow, Alduin writhes in agony and his soul begins to vanish. Alduin thrashes on the ground as his soul leaves his corporeal form. As his essence drains away, a black tar like skeleton is revealed underneath. His form continues to corrode, fading into wisps and with a final, thunderous spasm, Alduin is torn apart; not even his skeleton remains in this afterlife.
Tsun awaits.
As the mist of Alduin's soul snare dissipates and the sky clears, Tsun congratulates you on your mighty deed, as do your three helpers and all the characters lost in the mist, who will make their way to the bridge. Before leaving Sovngarde, Tsun teaches you the Call of Valor shout which allows you to summon a hero from Sovngarde to fight by your side. When you are ready to leave, talk to Tsun and he will shout you back to Tamriel.
You will be returned to the Throat of the World. Several dragons are perched there, all acknowledging the Dovahkiin and the destruction of Alduin World-Eater, and one by one they depart. If you did not already kill Paarthurnax, he will have a final conversation with you, and expresses hope to convince other dragons to join the Way of the Voice. Afterwards, if you are still on the mountaintop, Odahviing will come to admit his allegiance to you so that you may freely use his Thu'um to call him, though he warns that not all dragons are willing to follow Paarthurnax's example.
Congratulations! You have completed Skyrim's Main Quest, and may now continue your adventures.
