It's small, but Kathryn manages to briefly escape from the Lonely Mountain by drugging Smaug with strong sedatives she had forgotten in her pocket. After he recaptures her, she manages to talk him into sparing her and trusting her not to try to escape again so that he won't keep her in the birdcage for more than one night.
Simply managing to stay alive for nearly one full year as the prisoner of a wrathful, possessive and homicidal dragon is impressive in itself.
When Kathryn ends up in a possibly lethal vision involving Sauron and the War of the Last Alliance, Smaug enters the vision and helps her to get out of it.
As foolish as the Knight of Gondor was to try and vanquish Smaug with just the Eluvienel Bow as his aid, points for trying to free the land of the dragon.
When Kathryn sees three Orcs and a Warg surrounding Andraya and Freyja, she directs their attention towards herself. After she leaves herself exhausted and weaponless after killing two of the Orcs, Andraya and Freyja rescue her in return. The witch scorches the Orc by aiming a magical fireball at him, while the girl shoots the Warg in the eye with a crossbow.
Faervel makes his first appearance by defeating the four Mirkwood elves who are about to take Kathryn prisoner.
Just when Kathryn, exhausted and wounded by an arrow, is about to be captured by Bolg's Orcs, Smaug, sensing she's in danger through their bond, enters her mind and combines their magic to transform her into her dragon form for the first time. The golden dragoness then proceeds to annihilate the Orcs before having to return back to Kathryn.
Thorin's Company employs a bit more crafty strategy to kill Smaug than in The Desolation of Smaug where they, in essence, just try to drown him in molten gold. Here, they cause him to stand precariously on the edge of the shaft outside the forges, and when they bombard boulders and molten gold down on him, he falls down the shaft. When he reaches the bottom, he falls through it into the underground lake. The cold water causes the molten gold on his flesh to solidify, forcing him to act quickly and scrub the gold off before he becomes immobile underwater.
Tauriel helping Bard fight against Smaug. Even when he crushes most of her bones and she's helpless to prevent him from killing her, she refuses to beg for mercy and tells him in Elvish that he's a king only in his own imagination.
Smaug nearly bites Bard's leg off, with only Tauriel's interference saving the Bowman. Despite this, he's able to get to the still working windlance and use it to shoot the Black Arrow into Smaug's heart.
Kathryn tries to save Smaug from death by using her Raw Magic to heal him. She overexerts herself and dies. However, it ultimately turns out that her effort does save him as well as unwittingly transform him into a human.
Heart of Ashes
When King Wilhelm is angered by Smaug's "The Reason You Suck" Speech, he orders his guards to cut out the tongue of "Cail Agonn". Queen Lalemwen sternly puts her foot down and forbids blood to be shed in her father's throne room, seeming to stand up for herself for the first time in her court.
On Queen Lalemwen's orders, Smaug is taken to the dungeons. Kathryn is in turn taken to her chambers immediately afterwards, and surprise, he has already escaped and is waiting for her there.
Kathryn: What are you doing here?! You were taken — Smaug: Do not finish that sentence for it will only insult me that you believe I would even allow the notion of a pack of humans to keep me prisoner.
When Smaug runs from Vathvael in the midst of his Painful Transformation, Kathryn tells the guards keeping her confined in her chambers to bring her Faervel. When they refuse, she repeats her request in an assertive way before slamming the door in their faces, after which they obey. When one of them refuses to leave her alone with the elf, she scares him away with her glowing eyes.
After Smaug transforms into a half-man/half-dragon that acts like a wild animal, Kathryn manages to calm him down by singing to him. She then enters his mind and uses her magic to return him to a dragon.
During their last conversation, Lord Beronor demands utter obedience from Kathryn, threatening to make her life hard if she refuses. While still fearful of Beronor, the outraged Kathryn finally talks back to him.
Smaug kills four armed guards who try to attack him in Kathryn's bedchamber easily and without clothes. He's soon afterwards hit by three arrows while he's trying to turn back into a dragon, and while he's exhausted once the transformation is complete, he still easily overpowers Dorwinion's soldiers.
In the 15th chapter, Kathryn sees in a vision how Ancalagon the Black led the dragons on a devastating onslaught against the forces of the Valar, turning the tide of battle in Morgoth's favor.
Lord Beronor: Perhaps the general is tired. His mind is fevered from his wounds. Like us all, he is ageing and simply does not want to admit that he lost his battle against the dragon due to his lack of sound judgement due to age — General Victis: Bastard! [points his sword at Beronor's chest] I may be old and tired, aye. But I had PERFECT judgement when I was out there with my men! It was not my judgement that made the arrows bounce off of the brute's scales! It was not my old age that gave that creature such a deadly ferocity that it tore my men apart with little effort! If you believe that our army is sufficient to take it down, Beronor, then you won't mind when I volunteer you to be at the front line leading the men when the thing next comes!
At the end of that same scene, Queen Lalemwen decides to ask Erebor's Dwarves to create any Black Arrows they can for whatever price they ask. Lords Beronor and Gregorse try to protest against asking for help from the people they planned to "discreetly" conquer. The gentle, pregnant, and recently widowed Queen puts a stop to their nonsense in a way that makes Quithyra proud to serve Lalemwen.
Lord Beronor: Your Majesty! We cannot go to others and beg for help! The words of Dorwinion have always been 'Strong and sure'. Queen Lalemwen: I do not give a damn about words when my people are in danger! If that dragon returns, I want us to live long enough to say that we swallowed our pride to survive so that we might have any pride with which to speak of. Lord Beronor: Your Majesty, please listen to us when we say — Queen Lalemwen: [rises up to glare at the Lords] I am the Queen. You. Listen. ToMe!
Gandalf faces Smaug in the 21st chapter, holding his own well against the dragon. Smaug gives a look that indicates him to consider the wizard a Worthy Opponent.
The final fight. Fankil proves himself to be quick and tough enough to give Smaug a hard time.
When Kathryn arrives at the Door of Night under Fankil's control, Irmo frees her before giving her a power boost. When she wakes up in the physical world, she frees herself and fights Fankil, even taking the form of a dragon.
Heart of the Inferno
In the 7th chapter, Smaug faces Moria's Balrog in a vicious fight. Despite being at least twice as big, Smaug has to use his brain as much as his brawn. See here for the author's drawing.
While Smaug's facing the Balrog, Kathryn tries to resuscitate Gandalf by transferring Raw Magic into him. When the Balrog appears to loom over them, Gandalf temporarily wakes up to charge his sword with a thunderbolt and stab the Balrog's chest, after which Smaug finishes the creature off.
When Smaug refuses to help Lothlórien's Elves to repel the Orcs of Dol Guldur and leave Kathryn to endure her difficult labour, Galadriel changes his mind by suggesting that he's too cowardly to stand against Sauron. Smaug comes very close to devouring her in outrage, only to decide to prove he's no coward and swear to destroy Sauron for all the pain the Dark Lord has given him and Kathryn. The Lady of Lothlórien called Smaug the Golden a coward and got away with it!
Galadriel: Perhaps I was mistaken, then. Perhaps you are not the famed dragon-dread who could slay an army as he did the great warriors of old. Perhaps you are just a snake too craven to stand against the Dark Lord. [Smaug nearly attacks Galadriel, but then he ponders on what Sauron has done to him and Kathryn and makes up his mind] Smaug: For what Sauron has done, I vow to kill him and all that he rules for this insult!
When Urgost calls Kolstros and Vervenia unnatural half-breeds, Kathryn gives him in the chest a magical blast so powerful that he's almost driven back.
When Urgost earlier threatens Kathryn for refusing to look him in the eye, the twins leave their hiding place behind her to perch on her shoulders and hiss at Urgost even though they're scared themselves by the adult dragon.
Smaug defeats Urgost in battle rather quickly.
Smaug and Faervel's battle of wits in the 15th chapter that's borrowed from Star Trek Into Darkness. You can practically hear the shared actor of Smaug and Khan uttering the slightly different threats. But then, without losing his cool, Faervel calls upon the favour Smaug swore to him in the previous story and forces the dragon to accept King Brand's condition that Kathryn will be returned to him once he returns from the north and leaves Erebor and Dale without harming a single soul.
After Aragorn falls in the river during the fight against Saruman's Warg-riders, Kathryn saves him by briefly summoning Arwen to revitalize his will to live.
for the author's drawing.