- "It is not a matter of gold, this is blood magic. Only death pays for life."
- ―Mirri Maz Duur
Mirri Maz Duur promises Daenerys that she can save Drogo's life using blood magic, but she needs to sacrifice a life to save his. She takes Drogo's horse into his tent and slits its throat as the ceremony begins. Qotho becomes enraged as Daenerys attempts to save her husband and tries to attack Daenerys, but Ser Jorah kills him. Daenerys starts to go into labor, but none of the Dothraki midwives will help her, thinking she is cursed. With no choice, Jorah takes Daenerys into the tent where the blood ceremony is taking place.
In the wastelands beyond Lhazar, Daenerys wakes up to face terrible news from Ser Jorah Mormont. Her son, Rhaego, is dead. He was stillborn, a deformed monster with bat wings. The khalasar has moved on, leaving a small group behind. However, Drogo lives. Mirri Maz Duur takes Daenerys to see him, only to find him lying in a catatonic state. Daenerys demands to know why, and Duur explains that when Daenerys saved her, she'd already been raped three times, and Drogo's men had destroyed her temple and killed people she healed. She explains that she killed Rhaego for revenge and has prevented the Stallion Who Mounts the World from causing more destruction and suffering.
Stannis Baratheon burns in a brazier three leeches gorged on Gendry's blood - considered by Melisandre King's blood due to his status as Robert Baratheon's offspring - representing the three "usurpers" he wants destroyed: Robb Stark, Balon Greyjoy, and Joffrey Baratheon. By season 6, all of the aforementioned "usurpers" are dead: Robb Stark is killed at the Red Wedding; Joffrey Baratheon is poisoned at his own wedding; Balon Greyjoy is killed by his brother, Euron Greyjoy, on Pyke. It is unclear whether the leech ritual had anything to do with the three deaths, since none of them were caused by magical means.
For full information, see the main article about the "Leech Ritual"
When Cersei Lannister was young, she visited a Woods witch, called Maggy, who used blood magic to predict her future. Maggy had Cersei prick her finger with a knife, then Maggy sucked on her finger to taste the blood. From this she prophesied that Cersei would be queen and have three children, but that all three would predecease her, and eventually she would be deposed by a new and younger queen.
Melisandre warns Stannis Baratheon that a sacrifice must be made to the Lord of Light in order to save his army and keep marching towards Winterfell. She urges Stannis to sacrifice his daughter, Shireen Baratheon, in order to utilize her King's blood. Desperate to keep his army marching, Stannis reluctantly allowed his daughter to be burned at the stake as a sacrifice to the Lord of Light.