Tyene Sand is the third of the eight bastard daughters of Prince Oberyn Martell, known as the "Sand Snakes". She is also his eldest daughter by his paramour, Ellaria Sand. Tyene fights using duel-wielded daggers, though her other signature weapon is her skill with poisons - a trait she inherited from her father. Like her father, she is known to coat her blades with poisons, making a single scratch lethal.
Tyene can feign being soft-spoken and childlike, but this is just an act to keep her enemies off guard, as she is just as fierce as her older sisters.
Tyene is the youngest of the four adult Sand Snakes, and more impetuous than her older sisters Obara and Nymeria. Where Obara will face threats head-on (confident in her martial prowess), and Nymeria will stand back and analyze the situation to make a precise strike at her enemy's weak points, Tyene tends to heedlessly charge ahead. This is exemplified by her choice of daggers as her main hand-held weapon: they are quick on the draw, allowing her to lash out quickly, before even her older sisters can restrain her
Oberyn mentions his eight bastard daughters to Queen Cersei Lannister
When Ellaria Sand goes to the Water Gardens to scold Doran for his inaction to Oberyn's murder, she tells the Prince that Dorne must go to war against the Lannisters, and points out that the Sand Snakes, who have the love of their people, agree with her, and that they will avenge their father if Doran does not
Tyene, Nymeria, and Obara meet with Ellaria, who embraces her daughter Tyene warmly. They discuss rallying Dorne to go to war against House Lannister. When the conversation shifts to Myrcella Baratheon, Obara reveals information she received from a merchant captain that Jaime Lannister has been smuggled into Dorne. Ellaria insists that they must stop Jaime from reaching Myrcella. They are presented with a choice: side with Doran and have peace, or side with Ellaria and have war. Tyene is the first to speak, saying she will always side with her mother, and then Nymeria and Obara also agree to side with Ellaria.
When the Sand Snakes make their attempt to kidnap Myrcella, Tyene battles Bronn with the help of her sister Nym while Obara goes after Jaime Lannister herself while her sisters battle Bronn. Although she manages to wound Bronn in the arm with one of her daggers, the battle is quickly broken up by Areo Hotah and the rest of Doran's personal guard. After a tense confrontation, Obara commands her sisters to drop their weapons, and Tyene does so. They, along with Jaime, Bronn and Ellaria Sand, are taken into custody.
The Sand Snakes are imprisoned for their part in Myrcella's attempted kidnapping, with Bronn in the cell next to them. Tyene seduces Bronn from behind the bars of her cell, all while asking about the cut she inflicted on him during their earlier fight. Unknown to Bronn, Tyene coated her daggers with a poison called The Long Farewell, and her attempts to seduce him were in an effort to raise his heart rate, hastening the poison's course through his body. His vision blurs, his nose bleeds, and he collapses along a wall in his cell. Tyene removes an ampoule containing the antidote from her necklace and offers it to Bronn, but only if he tells her that she is the most beautiful woman in the world. Barely coherent, he replies that she is, and is thrown the ampoule. He manages to drink it before passing out.
As Tyene and Nymeria are playing a game of reflexes with each other, Areo Hotah arrives at their prison cell to escort the three Sand Snakes to the Water Gardens. Tyene is forced to watch along with the other Sand Snakes as Prince Doran forces Ellaria to swear her allegiance to him in the Water Gardens, bound at the wrist.
Tyene and her sisters later watch as Princess Myrcella departs for King's Landing along with Jaime, Bronn, and Prince Trystane. Tyene sexually jokes with Bronn and promises that they may see each other again. After Ellaria seals Myrcella's fate with a poison kiss, Tyene offers a cloth for her mother to wipe the blood from her nose, an effect from the poison coated on her lips, as they watch Myrcella's boat from afar. Though the young Lannister is killed, Ellaria surives, drinking up the antidote.
Tyene and Ellaria are with Doran when a maester appears to deliver a message, bearing news of Ellaria's murder of Myrcella. Before the prince has a chance to react Tyene stabs Areo Hotah in the spine, killing him immediately before Ellaria assassinates Doran.
Months later, Tyene is present with her sisters when Ellaria meets with Olenna Tyrell in the Water Gardens. The Queen of Thorns shuts down Tyene when she attempts to speak, demanding that the "grown women" speak without interruption. Ellaria claims that Dorne and House Tyrell must work together for justice and vengeance, as Queen Cersei has declared war on both of their factions. Varys then appears, claiming that they will defeat Cersei with "Fire and Blood", making it clear that Ellaria, the Sand Snakes, and House Tyrell will support Daenerys Targaryen's claim to the Seven Kingdoms.
Daughter of Oberyn Martell with Ellaria Sand, Tyene is the youngest of the Sand Snakes. Tyene is proficient with daggers and is fully aligned with her mother's quest to avenge Oberyn's death.