The magic of the Old Gods/Greenseers/Children of the Forest and the use of their heart trees/weirwood trees is one of the more interesting subjects in the series. With that in mind I thought it would be fun to discuss the use of weirwood as a physical weapon.

The Use of Weirwood Weapons in the Series

We know that weirwood is expensive and rare and does not rot:

Inside were floors and pillars of milky white marble veined with gold; the rafters overhead were carved from the bone-pale trunks of weirwoods. Dunk could not begin to imagine what all of that had cost. -The Mystery Knight

and:

"The Brackens poisoned it," said his host. "For a thousand years it has not shown a leaf. In another thousand it will have turned to stone, the maesters say. Weirwoods never rot." -ADWD, Jaime I

And while the above quotes aren't necessarily about weapons, they speak to the strength of the wood.

Ygritte

Ygritte is a wildling spearwife/warrior woman, who carries a short curved weirwood bow.

Ygritte trotted beside Jon as he slowed his garron to a walk. She claimed to be three years older than him, though she stood half a foot shorter; however old she might be, the girl was a tough little thing. Stonesnake had called her a "spearwife" when they'd captured her in the Skirling Pass. She wasn't wed and her weapon of choice was a short curved bow of horn and weirwood, but "spearwife" fit her all the same. She reminded him a little of his sister Arya, though Arya was younger and probably skinnier. It was hard to tell how plump or thin Ygritte might be, with all the furs and skins she wore. -ASOS, Jon II

Bloodraven

Although Bloodraven carried/"carries" the Valyrian sword Dark Sister, his favorite weapon was a weirwood bow:

Bloodraven is described in "The Sworn Sword," so I won't repeat that here. He's tall and wiry, but sscrawny compared to his magnificent half-brothers. Although a good swordsman, his main weapon is the bow; he has a tall longbow made of weirwood, and fires white weirwood arrows fletched with raven feathers. He is also, by repute, a sorcerer. Sharp features, vaguely sinister. -SSM, Concerning the Great Bastards: 6 April 2004

The Raven's Teeth

Bloodraven's personal guard, carried weirwood bows as well:

From Maidenpool had come Lord Mooton, from Raventree Lord Blackwood, from Duskendale Lord Darklyn. The royal demenses about King's Landing sent forth Hayfords, Rosbys, Stokeworths, Masseys, and the king's own sworn swords, led by three knights of the Kingsguard and stiffened by three hundred Raven's Teeth with tall white weirwood bows. Mad Danelle Lothston herself rode forth in strength from her haunted towers at Harrenhal, clad in black armor that fit her like an iron glove, her long red hair streaming. The light of the rising sun glittered off the points of five hundred lances and ten times as many spears. The night's grey banners were reborn in half a hundred gaudy colors. And above them all flew two regal dragons on night-black fields: the great three-headed beast of King Aerys I Targaryen, red as fire, and a white winged fury breathing scarlet flame. Not Maekar after all, Dunk knew, when he saw those banners. The banners of the Prince of Summerhall showed four three-headed dragons, two and two, the arms of the fourth-born son of the late King Daeron II Targaryen. A single white dragon announced the presence of the King's Hand, Lord Brynden Rivers. -The Mystery Knight

Brandon Snow

While not confirmed, it is theorized that Brandon Stark intended to attempt to slay Aegon I's dragons using arrows from the Winterfell weirwood tree:

After that the glimpses came faster and faster, till Bran was feeling lost and dizzy. He saw no more of his father, nor the girl who looked like Arya, but a woman heavy with child emerged naked and dripping from the black pool, knelt before the tree, and begged the old gods for a son who would avenge her. Then there came a brown-haired girl slender as a spear who stood on the tips of her toes to kiss the lips of a young knight as tall as Hodor. A dark-eyed youth, pale and fierce, sliced three branches off the weirwood and shaped them into arrows. The tree itself was shrinking, growing smaller with each vision, whilst the lesser trees dwindled into saplings and vanished, only to be replaced by other trees that would dwindle and vanish in their turn. And now the lords Bran glimpsed were tall and hard, stern men in fur and chain mail. Some wore faces he remembered from the statues in the crypts, but they were gone before he could put a name to them. -ADWD, Bran III

and:

Torrhen's scouts had seen the ruins of Harrenhal, where slow, red fires still burned beneath the rubble. The King in the North had heard many accounts of the Field of Fire as well. He knew that the same fate might await him if he tried to force a crossing of the river. Some of his lords bannermen urged him to attack all the same, insisting that Northern valor would carry the day. Others urged him to fall back to Moat Cailin and make his stand there on Northern soil. The king's bastard brother Brandon Snow offered to cross the Trident alone under cover of darkness, to slay the dragons whilst they slept. -TWOIAF, The Reign of the Dragons: The Conquest

Alysanne Blackwood

Another member of House Blackwood, another good archer. Alysanne aka Black Aly was a highborn warrior woman who ended up marrying Cregan Stark. She avenged her brother in the Dance of the Dragons by killing the Bracken who killed him (supposedly):

Ser Amos Bracken, leading the host from Stone Hedge, cut down and slew Lord Blackwood in single combat, only to perish himself when a weirwood arrow found the eye slit of his helm and drove deep into his skull. Supposedly the shaft was loosed by Lord Samwell's sixteen-year-old sister , Alysanne would later be known as Black Aly, but whether this is fact or mere family legend cannot be known. -Fire & Blood I, The Dying of the Dragons: The Red Dragon and the Gold

The Children of the Forest

The children were said to use weirwood bows:

"They were a people dark and beautiful, small of stature, no taller than children even when grown to manhood. They lived in the depths of the wood, in caves and crannogs and secret tree towns. Slight as they were, the children were quick and graceful. Male and female hunted together, with weirwood bows and flying snares. Their gods were the gods of the forest, stream, and stone, the old gods whose names are secret. Their wise men were called greenseers, and carved strange faces in the weirwoods to keep watch on the woods. How long the children reigned here or where they came from, no man can know. -AGOT, Bran VII

and:

The giants had no kings and no lords, made no homes save in caverns or beneath tall trees, and they worked neither metal nor fields. They remained creatures of the Dawn Age even as the ages passed them by, men grew ever more numerous, and the forests were tamed and dwindled. Now the giants are gone even in the lands beyond the Wall, and the last reports of them are more than a hundred years old. And even those are dubious—tales that rangers of the Watch might tell over a warm fire. The children of the forest were, in many ways, the opposites of the giants. As small as children but dark and beautiful, they lived in a manner we might call crude today, yet they were still less barbarous than the giants. They worked no metal, but they had great art in working obsidian (what the smallfolk call dragonglass, while the Valyrians knew it by a word meaning "frozen fire") to make tools and weapons for hunting. They wove no cloths but were skilled in making garments of leaves and bark. They learned to make bows of weirwood and to construct flying snares of grass, and both of the sexes hunted with these. -TWOIAF, Ancient History: The Dawn Age

Styr

The Magnar of Thenn carries a weirwood spear:

It was then that he saw Styr. The Magnar was climbing up the barricade, over the gutted corn sacks and smashed barrels and the bodies of friends and foe alike. His bronze scale armor gleamed darkly in the firelight. Styr had taken off his helm to survey the scene of his triumph, and the bald earless whoreson was smiling. In his hand was a long weirwood spear with an ornate bronze head. When he saw the gate, he pointed the spear at it and barked something in the Old Tongue to the half-dozen Thenns around him. Too late, Jon thought. You should have led your men over the barricade, you might have been able to save a few.

Morna White Mask

Morna is considered a witch, and its probable that her mask is more ceremonial than armor:

Howd Wanderer swore his oath upon his sword, as nicked and pitted a piece of iron as Jon had ever seen. Devyn Sealskinner presented him with a sealskin hat, Harle the Huntsman with a bear-claw necklace. The warrior witch Morna removed her weirwood mask just long enough to kiss his gloved hand and swear to be his man or his woman, whichever he preferred. And on and on and on. -ADWD, Jon XII

Thoughts/Theories

• So many members of House Blackwood seem to use them
• Since dragons are vulnerable in the eye, its possible Brandon Snow knew what he was doing, especially if some how these arrows are powered by the magic of the old gods
• We see this quote about Bloodraven and the Raven's Teeth using the bows:

"The hammer and the anvil?" The old man's mustache gave a twitch. "The singers leave out much and more. Daemon was the Warrior himself that day. No man could stand before him. He broke Lord Arryn's van to pieces and slew the Knight of Ninestars and Wild Wyl Waynwood before coming up against Ser Gwayne Corbray of the Kingsguard. For near an hour they danced together on their horses, wheeling and circling and slashing as men died all around them. It's said that whenever Blackfyre and Lady Forlorn clashed, you could hear the sound for a league around. It was half a song and half a scream, they say. But when at last the Lady faltered, Blackfyre clove through Ser Gwayne's helm and left him blind and bleeding. Daemon dismounted to see that his fallen foe was not trampled, and commanded Redtusk to carry him back to the maesters in the rear. And there was his mortal error, for the Raven's Teeth had gained the top of Weeping Ridge, and Bloodraven saw his half brother's royal standard three hundred yards away, and Daemon and his sons beneath it. He slew Aegon first, the elder of the twins, for he knew that Daemon would never leave the boy whilst warmth lingered in his body, though white shafts fell like rain. Nor did he, though seven arrows pierced him, driven as much by sorcery as by Bloodraven's bow. Young Aemon took up Blackfyre when the blade slipped from his dying father's fingers, so Bloodraven slew him, too, the younger of the twins. Thus perished the black dragon and his sons. -The Sworn Sword

• Galon Whitestaff was an extremely influential Ironborn priest who carried a staff made of weirwood or nagga's bones depending on the tale.
• Weirwood bows seem to be quite powerful, I think we can potentially assume that they are only outdistanced/ranged by bows made of dragonbone and goldenheart (Sarella/Alleras has one)

A third of Balaq's men used crossbows, another third the double-curved horn-and-sinew bows of the east. Better than these were the big yew longbows borne by the archers of Westerosi blood, and best of all were the great bows of goldenheart treasured by Black Balaq himself and his fifty Summer Islanders. Only a dragonbone bow could outrange one made of goldenheart. Whatever bow they carried, all of Balaq's men were sharp-eyed, seasoned veterans who had proved their worth in a hundred battles, raids, and skirmishes. They proved it again at Griffin's Roost. -ADWD, The Griffin Reborn

and:the princes of the isles have forbidden the export of goldenheart wood since the Slavers' Wars; only bows of dragonbone are known to surpass them, and those are exceedingly rare. -TWOIAF, Beyond the Free Cities: The Summer Isles

• On the show, the Night King kills a dragon with a magical spear/blade, While this is likely based on the ice swords of the Others, its possible it could be based on a spear/arrow of weirwood and a dragon's eye (and they could be the same thing). We will see.
• It should be noted that we do have this quote that could potentially (depending on how you read it) counter some of the above thoughts:

"The godswood." Meera Reed ran after the direwolf, her shield and frog spear to hand. The rest of them trailed after, threading their way through smoke and fallen stones. The air was sweeter under the trees. A few pines along the edge of the wood had been scorched, but deeper in the damp soil and green wood had defeated the flames. "There is a power in living wood," said Jojen Reed, almost as if he knew what Bran was thinking, "a power strong as fire." -ACOK, Bran VII

I looked relatively hard, but really couldn't come up with any other instances of weirwood type weapons (unless you count the Other's swords, but that gets into a discussion for another day) We see weirwood used for bowls, doors, tables, etc.

It would be interested to see if the crannogmen used it, but I didn't see anything with regards to their weaponry/weirwoods, even though their magic is similar and they probably share DNA.

TLDR: A list of weirwood weapons used in the series and some thoughts/theories about it.