Dragonslayer

Alduin's Mist
When you leave the Hall of Valor and cross the bone bridge, your next objective is to get rid of the mist in the valley. The three heroes will line up and you have to equip the Clear Skies shout.You need to use Clear Skies shout 3 times as Alduin will summon the mist 2 times.

Felldir: We cannot fight the foe in this mist!

Gormlaith: Clear Skies - combine our Shouts!

Gormlaith: Again!

Alduin:

Felldir: We can shatter his power if we Shout together!

Alduin: Ven Mul Riik!

Hakon: Does his strength have no end? Is our struggle in vain?

Gormlaith: Stand fast! His strength is failing! Once more, and his might will be broken!

Felldir: His power crumbles - do not pause for breath!

Use it and the 3 heroes will use it as well. After Alduin summons the mist again, use it again until the heroes use it as well. Alduin will now summon the mist for the last time. After a small dialogue use the Clear Skies shout for the last time. This will get rid of the mist and Alduin will appear. It would be wise to save when he appears, so you won't have to do all of this again if you die.

Alduin's Fall
Now that Alduin has appeared it is your job to kill him. Use your Dragonrend shout on him as soon as possible. Attack him when he's on the ground. Use your Dragonrend shout as much as possible to stun him and keep the other heroes alive. If you're low-leveled and can't kill Alduin before he "defeats" the other three heroes, be ready to use lots of healing potions or spells, as his fire breath attack is quite strong. A simple tactic to defeat Alduin is to use the same tactic you may have used against him in the fight at the Throat of the World. A shield bash/stun will stop him from using his fire breath along with using the unrelenting force shout, and in between shield stuns, it should be possible to get two to three swings with a weapon in. Between using Dragonrend and stunning him, it should be a simple matter of ensuring your life doesn't drop too low from his physical attacks, and maintaining your stamina to use the shield bash.

Tsun: That was a mighty deed! The doom of Alduin encompassed at last, and cleansed is Sovngarde of his evil snare. They will sing of this battle in Shor's hall forever. But your fate lies elsewhere. When you have completed your count of days, I may welcome you again, with glad friendship, and bid you join the blessed feasting.

All: All hail the Dragonborn! Hail him/her with great praise!

Tsun: Return now to Nirn, with this rich boon from Shor, my lord: a Shout to bring a hero from Sovngarde in your hour of need.

Quotes

 * I have already defeated your friends once. . I do not fear them.
 * I have already defeated your friends once. . I do not fear them.
 * I have already defeated your friends once. . I do not fear them.
 * I have already defeated your friends once. . I do not fear them.
 * I have already defeated your friends once. . I do not fear them.

Bugs

 * Some of the optional Souls may cause the quest to glitch, not allowing you to help any of the other souls through the fog. This seems to happen mainly with the first Stormcloak you meet on the path.
 * After the main quest has been completed, Radiant AI seems to increase all dragons spawning rate by almost 200% making fast traveling nearly impossible without encountering a dragon, it is unknown if this is a glitch.
 * After using Storm Call shout in Sovngarde the count down bar for shouting again becomes locked and will not let you clear skies to fight Alduin.
 * It's possible to make returning to Skyrim impossible: Throw Tsun to the giant waterfall by making him follow you near the bone bridge. Talk to him so that he faces the opposite of the fall, and cast two-handed destruction spells to him (with Impact perk activated) so that he drops down below. If you try to follow, you'll die instantly.
 * After using "clear skies" the required number of times, Alduin still does not turn up. Re-load earlier save files until he does.

Gallery
Drachentöter Matadragones Ammazzadraghi Драконоборец