"Any man dies with a clean blade . . . I'll rape his fucking corpse!"
The Hound was in his element, hacking apart the poor sods unfortunate enough to charge the gates. The screams of the dying were almost music to his tortured soul. Blood caked his sword, and his armour, and his helmet for which he was known, a snarling hound, teeth bared, ready for the kill. Stannis Baratheon and whatever was left of his fleet was attacking the Mud Gate, hoping to break through and sack the city. Technically it was his by rights, Joffrey was an inbred bastard and only king by the strength of his grandfather's army. Said army was currently somewhere in the Riverlands, and of absolutely no use to anyone at the minute. The City Watch and whatever men the Queen Regent had left would have to do. A bunch of frightened boy-whores, the lot of them. Fear of him kept the defenders fighting on to the last gasp, none wanting him to make good on his terrifying promise.
Suddenly, a piece of ball-lightning* appeared out of nowhere, crashed into him, and everything went to shit.
Without the Hound to inspire the men, the gates soon fell. As men stood scratching their arses, wondering what had happened, Stannis's men, who were just as confused, but far better trained, charged forward and hacked the defenders apart. Joffrey couldn't flee the scene fast enough, but his uncle, Lord Tyrion, the Imp, held the gates and the wall as long as was feasible, before an armoured gauntlet smashed into his face and everything went dark.
Stannis took the city a little over an hour later, and not a moment too soon, as the absent Tywin Lannister finally arrived with the Knights of the Reach, all in splendid, expensive armour and gleaming swords, only to face closed gates and an unfamiliar standard above the walls. As he soon realised, horses aren't all that great at climbing ladders, and so they began to besiege the city even as the men of the Burning Stag moved to hold what they had just conquered. That might have been the end of it, were it not for the fearsome pirate, Salladhor Saan, who had been kept in reserve. He fired scorpion bolts into the disorganised cavalry, rained arrows down upon them, and sent them fleeing in a disorganised mess. Tywin Lannister was found the next morning, trampled to death. His mourners were few and far between.
Stannis took Maegor's Holdfast without too much difficulty, grinding his teeth over the dead body of his no-longer-nephew Tommen. He was a sweet boy, weak to be sure, but with none of the Lannister poison. Joffrey, on the other hand, was captured alive and burned at the stake, screaming curses and begging mercy in equal measure. A vicious, evil coward to the end. His mother, who had poisoned her other son with nightshade to spare him this fate, soon followed. The witch prattled on about her Fire God, and Stannis took a moment to think. R'hllor played no part in this victory. Men took the city, men held the city, and these executions reminded him unfavourably of the Mad King Aerys Targaryen. She had power, to be sure, but it was time to put a stop to this nonsense. He drew his sword and calmly walked forward, beheading his late brother's wife before the flames reached too high, unknowingly imitating a certain Archon from a world he had never heard of.
The following months brought much peace and stability to the region. Robb Stark eventually bent the knee and surrendered his crown after many long peace talks, and quite a large serving of humble pie. Sansa went home, bringing Ice with her, though she was not the same girl the family remembered. Arya turned up at Riverrun, and it was a day of great rejoicement, though she too had seen things that could not be unseen. Through great trial and error, the Stark family healed, especially with the return of Rickon, though they never saw Bran again.
Walder Frey sat and stewed in his keep, but never, thankfully, hosted a wedding again in his lifetime.
Tyrion survived the battle, and was forced to become a Maester of the Citadel, having little difficulty earning his chain, though he viewed the oath of celibacy as a polite suggestion, and frequently visited places of ill repute. Shae did not go with him, and he never loved again.
Eventually The Wall came under attack from both Wildlings and the White Walkers, but both were stopped in their tracks by the combined might of Westeros, and something approaching a happy ending came about for most people.
But none of that really matters, this is about Ferelden, the Blight, and the most unethical Grey Warden in the history of Thedas. Sandor Clegane brought Ferelden into a new age, kicking and screaming when necessary, and his legend lived in infamy long after his death, with ruggedly handsome dwarves adding fantastical details with every telling.
*Look it up. No-one knows what it does, and it's as good a world-hopping plot device as any.