The Bifrost Bridge is a dimensional energy which allows instantaneous travel within the Nine Realms. It was used primarily by the Asgardians, who were able to use a Rainbow Bridge to harness the energy and access the Bifrost in order to travel to and protect those realms. The Bifrost was also able to be called upon using dark magic and was also imbued into Stormbreaker, allowing its wielder and any in its vicinity to access the bridge at any time. The immense dimensional energy, given enough concentration, could also be used to destroy planets.
- "If your return threatens the safety of Asgard, Bifrost will remain closed to you. And you'll be left to die in the cold waste of Jotunheim."
"Couldn't you just leave the bridge open for us?"
"To leave the bridge open would unleash the full power of the Bifrost and destroy Jotunheim, and with you upon it."
- ―Heimdall and Volstagg
Thor, Loki, Sif and the Warriors Three decided to use the Bifrost Bridge to reach Jotunheim and attack the Frost Giants by surprise following an unexpected breach of Odin's Vault. Loki prepared to deceive Heimdall, however the Bridge's guardian, knowing their intent and curious as to how the Jotuns had slipped by him, allowed them into the Observatory. After activating the Bridge, Heimdall informed them that if their return threatened Asgard, he would keep the Bifrost closed to them, and informed Volstagg that the Bifrost's energy would eventually destroy Jotunheim if left open when the rotund warrior suggested that he leave it open for them.
As they fled from the Frost Giants, Loki, Sif and the Warriors Three returned to the Bifrost site, asking Heimdall to open the Bridge to allow their way, although to no response. Only when they and Thor were completely surrounded did the Bifrost open, allowing Odin, riding Sleipnir, to arrive. After Laufey refused the Allfather's request to excuse his son's and friends' incursion, Odin signaled for the bridge's activation, and the Asgardians were pulled back to their home realm.
Banished to New Mexico
Upon their return to Asgard, Heimdall was dismissed from his post by Odin as he and Thor argued. Odin proceeded to use Gungnir to activate the Bifrost, stripping Thor of Mjølnir, his armor and his power and banishing him to New Mexico on Earth, to be found by Jane Foster and her colleagues.
Later, in order to prove himself worthy of the throne of Asgard and distance himself from his Frost Giant heritage, Loki decided to use the Bifrost Bridge to completely destroy Jotunheim. Loki used the Bifrost to travel to Jotunheim so that he could forge a false alliance himself with Laufey, offering him access to Asgard through the Bifrost Bridge rather than one of his secret pathways.
Heimdall was suspicious of Loki's disguised actions while away, having been unable to see him with his omni-sense, and in response Loki ordered him to keep the Bifrost closed until he had dealt with the issues caused by Thor.
Knowing that Loki was acting out of his own selfish interests, Heimdall's omni-sense allowed him to learn that Sif and the Warriors Three wanted to use the Bifrost to reach Earth to rescue Thor and bring him back to Asgard after his banishment. Skirting Loki's order to not allow any through the Bifrost, Heimdall instead left Hofund behind for them to use.
Used as a Weapon
Having seen the Bifrost being activated, Loki decided to send the Destroyer to New Mexico to eliminate Thor and his allies to ensure his rule. After confronting Heimdall, Loki declared that he was relieved of duty and then froze him using the Casket of Ancient Winters. Using Gungnir, Loki activated the Bifrost to send the Destroyer to Earth, and after it was defeated, opening the Bifrost to Jotunheim, welcoming Laufey and a few of his men to Asgard. 
Once Heimdall was able to break free of the ice, he opened the Bifrost Bridge to allow Thor and the others to return. After Thor confronted him in Odin's bedchamber, Loki returned to the Observatory to activate the bridge once again, intending to use Laufey's infiltration of Asgard as justification for the Frost Giants' destruction. Once the Bifrost was opened to Jotunheim, Loki used the Casket to freeze the energy, so that its power would continue to build until Jotunheim was destroyed.
As Loki and Thor dueled on the Rainbow Bridge, the Bifrost continued to launch its full power at Jotunheim, the effects of which began to be visible on other worlds in the Nine Realms. Unable to get close enough the Observatory in order to shut it down, Thor realized he had to destroy the Rainbow Bridge, bringing Mjølnir down with full force and shattering it. After it was destroyed, the Bifrost Bridge could no longer be harnessed, preventing the annihilation of the Frost Giants, and creating a temporary wormhole which Loki allowed himself to fall through after Odin condemned Loki's actions.
Out of Action
With the Rainbow Bridge destroyed, preventing Asgard from harnessing the Bifrost and leaving them cut off from the rest of the Nine Realms, several Marauders began attacking the more peaceful of the unprotected realms.
Because of the Rainbow Bridge's destruction, Odin was forced to use dark magic to harness the Bifrost, at the cost of both of their health, to send Thor to Earth in order to retrieve Loki, who was attempting to use the Tesseract to conquer Earth.
Reestablishing Contact with the Nine Realms
Once Thor returned with Loki and the Tesseract, the Asgardians were able to regenerate the Rainbow Bridge using the energy obtained from the cube, thus granting them access to the Bifrost once more. The Tesseract was then placed under the care of Heimdall, who resumed his position as gatekeeper of the bridge.
Thor and his friends used the Bifrost Bridge multiple times to pacify the Nine Realms, the last campaign of which sent them and several Einherjar to Vanaheim. Thor arrived after the battle had already begun, launching Mjølnir at a Marauder while the bridge was still open. 
Once the Marauders were defeated, Volstagg, Fandral and the Einherjar began transporting their prisoners back to Asgard through the Bifrost for imprisonment, transporting dozens at a time. In order to infiltrate Asgard, the Dark Elf Algrim disguised himself as a Marauder so that he was transported amongst their prisoners.
Temporary Shut Down
Following the Dark Elves' first attempt assault in their War against the Asgardians, Odin ordered the Bifrost shut down to prevent anyone from leaving, forcing Thor to ally with Loki in order to find another way off Asgard.
Thor used the Bifrost Bridge to reunite with Jane Foster days after the resolution of the Dark Elf Conflict and the death of Malekith.
Loki's Disguised Reign
Sif used the Bifrost Bridge to come to Earth when she was chasing the criminal Lorelei. After her capture, the duo used the bridge to return to Asgard. A year later, she used the Bifrost Bridge to transport the Kree agent Vin-Tak from Earth.
Return from Muspelheim
With Heimdall banished from Asgard, Loki employed Skurge to take his place as Guardian of the Bifrost, who used the Bifrost to travel to the Nine Realms, visiting Texas and acquiring two assault rifles. While Skurge was operating Heimdall's Observatory, Thor called on Heimdall to help teleport him safely back to Asgard, though Skurge was at the time was attempting to impress two Asgardian women in the Observatory. Eventually one of the women pointed out the request to use the Bifrost; however, Skurge was unaware that Thor was concurrently being chased by a Fire Beast on Muspelheim. Upon activating the Bifrost, Skurge returned Thor to Heimdall's Observatory, but also inadvertently the head of the Beast who happened to be in the Bifrost's scope of teleportation.
Thor and Loki used the Bifrost to travel to New York City in order to find their father. However, upon Odin's later untimely demise in Norway, Hela was released from her imprisonment. After witnessing her destroy Mjølnir effortlessly, Loki called for safe passage through the Bifrost back to Asgard at once. When the Bifrost's beam reached the ground, Hela just managed to step into the light and enter the Bifrost, which ensued a skirmish between her, Loki, and Thor. She manifested blades while inside the Bifrost, quickly thrusting Loki out of the light and into the void, and soon did the same to Thor, inadvertently causing the pair to emerge on Sakaar, albeit at different times. 
Hela arrived on Asgard and immediately slew Volstagg and Fandral, who were guarding the Bifrost with Skurge, before moving to take control of Asgard. As she did so, Heimdall infiltrated the Observatory and stole Hofund in order to prevent the Bifrost from being used to assist Hela's plans to conquer the Nine Realms and the worlds beyond. Heimdall attempted to use the Bifrost to evacuate the Asgardians to another planet, although their path was thwarted by Hela's Berserker Army and her pet wolf Fenris. After Thor, Loki and Valkyrie returned to Asgard and engaged in combat with Hela, they realize that they are not able to defeat her since Hela's power only grew the longer she remained on Asgard, Thor realized that they had to allow Ragnarök to occur in order to defeat her. Once Loki threw Surtur's crown into the Eternal Flame, the fire demon was restored and granted his full power. As Surtur thrust his blade into Asgard, destroying it, the Rainbow Bridge was destroyed as well, forcing the Asgardians to use the Statesman to evacuate their planet since they could no longer harness the Bifrost.
Heimdall's Last Bridge
The ship transporting the Asgardians was attacked by Thanos and his ship, the Sanctuary II, and in the ensuing massacre Heimdall was wounded. After Thanos knocked out the Hulk, Heimdall used his final strength to muster enough dark magic to summon a Bifrost Bridge, which transported the green Avenger to the New York Sanctum.
Thor's Return to Earth
Through the power of his newly forged weapon, Stormbreaker, Thor was able to summon the power of the Bifrost to transport himself, Rocket Raccoon and Groot to Wakanda, arriving in the midst of the Battle of Wakanda.
The Bifrost Bridge is a transit system used by Asgardians to travel to the various realms among the Nine Realms and numerous other planets. The Bifrost uses a powerful, rainbow-like energy drawn from the center of Asgard to create Wormhole-like portals that can instantaneously transport people and objects between realms, over millions of light-years of distance. On other realms, the Bifrost appears as a brilliant beam of white light that shines down on its surface, often leaving behind a rune-like pattern burned into the ground.
The Bifrost Bridge is composed of two physical structures in Asgard; Heimdall's Observatory and the Rainbow Bridge, which act as two components of a large machine that channels energy from Asgard to create the portals that allow for transportation. The Rainbow Bridge draws energy from the center of Asgard to Heimdall's Observatory where it is directed to its destination allowing transportation that is precise and accurate. The Bifrost also behaves like a tractor beam, drawing people and objects bathed in its light back to Heimdall's Observatory, such as people wishing to reach Asgard or pulling the Aether from Svartalfheim to prevent Malekith from using it. The beam of energy projected by the Bifrost is powerful enough to destroy a realm/planet if it is allowed to remain open long enough, as Loki tried to do to Jotunheim.
|Appearances for Bifrost Bridge|
In chronological order:
- Not to be confused with the Rainbow Bridge, the Bifrost is the portal generated from Heimdall's Observatory that allows for transport between the Nine Realms.
- However, Thor once described the Bifrost as a rainbow bridge, due to the prismatic energy of the Bifrost resembling a rainbow.
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Thor
- ↑ Official Marvel Website MCU description for Loki
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Thor: The Dark World Prelude
- ↑ Thor: The Dark World Prelude, Volume 1
- ↑ The Avengers
- ↑ Agents of S.H.I.E.L.D.: 1.15: Yes Men
- ↑ Agents of S.H.I.E.L.D.: 2.12: Who You Really Are
- ↑ Avengers: Age of Ultron
- ↑ 9.0 9.1 9.2 Thor: Ragnarok
- ↑ 10.0 10.1 Avengers: Infinity War
- ↑ The Art of Thor