|Although this article is based on canonical information, the actual name of this subject is pure conjecture.
Joffrey's crossbow is a specialized crossbow that requires little effort to reload. It is currently owned by Bronn. It was commissioned by Joffrey Baratheon. It has a golden lion, the sigil of House Lannister, on the prod.
Before leaving on a hunting trip, Joffrey summons Margaery to his chambers. As she enters, he is holding his new crossbow. He asks if she likes it, and boasts that it is one of the finest weapons in Westeros. She asks to be shown how it works, and he explains that it is reloaded with a lever instead of a crank, much easier and faster than a regular crossbow. After loading, he shoots a bolt through the eyes of a wall-mounted boar's head, displaying that he has some skill with it. He then lets her hold the crossbow, and she manipulates him by humoring his sadistic tastes.
After escaping from the Black Cells (and hence execution for Joffrey's murder), Tyrion steals the crossbow from the Tower of the Hand. After murdering Shae, he finds his father Tywin in a privy, and kills him with two cross-bolts (one to the stomach and a final, fatal bolt to the heart), after dismissing Shae as a whore.
Bronn finds Tyrion and Jaime in the winter town, intending to kill them with the crossbow. He fires a warning shot at Jaime when he tries to call his bluff. However, when Tyrion promises Bronn Highgarden, which is much more valuable than Riverrun, he lets them live and leaves.
|Season Three appearances|
|Valar Dohaeris||Dark Wings, Dark Words||Walk of Punishment||And Now His Watch Is Ended||Kissed by Fire|
|The Climb||The Bear and the Maiden Fair||Second Sons||The Rains of Castamere||Mhysa|
|Season Four appearances|
|Two Swords||The Lion and the Rose||Breaker of Chains||Oathkeeper||First of His Name|
|The Laws of Gods and Men||Mockingbird||The Mountain and the Viper||The Watchers on the Wall||The Children|
|Season Eight appearances|
|Winterfell||A Knight of the Seven Kingdoms||The Long Night|
|The Last of the Starks||The Bells||The Iron Throne|
In the books
In the A Song of Ice and Fire novels, Joffrey occasionally uses a crossbow to shoot at animals (hares, cats) and people.
Tyrion gives Joffrey an ungainly Myrish crossbow that can shoot three quarrels at a time, just to rid himself of Joffrey. Joffrey uses it to frighten Sansa, boasting that he shot at people who came begging for food, hitting the loudest man right through the throat, and injuring a woman in the arm. He tells Sansa he'd shoot her too, but that would cost Jaime's life, so he "just" orders his guards to beat her up.
There is no indication that Tyrion uses the same crossbow to kill his father. The book makes a point that crossbow cannot be reloaded so easily and quickly as Tyrion does in the show.