"You can't stop it. The Bifrost will build until it rips Jotunheim apart." "Why have you done this?" "To do what Father never could. To destroy their kind forever. When he awakens, he'll see the wisdom of what I've done." "He won't! You can't kill an entire race!"
The Duel at the Bifrost Bridge was the final confrontration between Thor and Loki, where Thor fought his brother to prevent him from using the Bifrost Bridge in a plot to destroy Jotunheim, having to destroy the bridge itself to accomplish it.
"Now, if you'll excuse me, I need to destroy Jotunheim."
Loki learned that he was the son of the Frost Giant king Laufey, who abandoned him as a child to be found and raised by Odin, the king of the Asgardians. Since Thor was the "favorite son" of Asgard and destined to be its king, Loki felt rejected by both of his fathers. Loki invited Laufey to Asgard so he could kill Odin, who was incapacitated in his "Odinsleep", but Loki killed the Jotun King, doing something neither Odin or Thor would do.
"Loki, this is madness!" "Is it madness? Is it? Is it? I don't know what happened on Earth to make you so soft! Don't tell me it was that woman? Oh, it was. Well, when we're done here, maybe I'll pay her a visit myself!"
Loki activated the Bifrost to begin the destruction of Jotunheim by unleashing its full power. He explained that he only wanted to be Thor's equal in Odin's eyes, but now he desired the throne because he will have accomplished what no one else has done in destroying the Frost Giants. The two began to fight. As Loki fell onto the Rainbow Bridge, Thor placed Mjølnir on his chest, making him unable to move.
Loki taunted Thor that what he has set into motion was unstoppable. Meanwhile, Odin awoke from the Odinsleep.
Thor realized that Loki spoke the truth and began to hammer the Rainbow Bridge with Mjølnir. Loki told Thor that if the Rainbow Bridge was destroyed, Thor would never see Jane Foster again. Thor continued to pound the bridge until it collapsed. Both fell over the side, only to be caught by Odin.
Loki told his adopted father that he did everything to impress him. Odin listened, but disappointment showed on his face. Loki decided to release his grip and fell into Yggdrasil itself.
"With the Bifrost gone, how much dark energy did the Allfather have to muster to conjure you here?"