Many people have tried to exploit the Island throughout its history due to its special properties. People like Ben and Locke have also defended it from intruders and do not want anyone outside of the Island knowing of its location or its special abilities. Charles Widmore is desperately trying to find the Island and, according to Ben, exploit it, and has sent out a freighter crew to find it. However, in a conversation between Ben and Widmore, Widmore claims that the island was previously his, Ben stole it from him, and that he will take it back one day.
Similarly, Rose had been dying of cancer before crashing on the island. After the crash, she feels as if the cancer has "left her body" and credits her cure to the island ("S.O.S."). Sun becomes pregnant, despite the fact that a doctor had previously (secretly) declared her husband Jin to be sterile. When she informs Jin of the true diagnosis, Jin declares that the conception is a miracle ("The Whole Truth"). In the episode "D.O.C.", Juliet reveals that men on the island have five times the normal sperm count, explaining why Jin was able to impregnate Sun.
Despite his apparent death when John Locke pushes him through the invisible security fence surrounding the Others' encampment in the episode "Par Avion," Mikhail Bakunin later returns and stops the internal bleeding of the helicopter pilot, Naomi. He claims she will be fine in about a day, much to Charlie's surprise. That being far less than the normal recovery time for such an injury, Mikhail states that "things work differently" on the island. In the episode, "The Man Behind the Curtain," Mikhail tells Ben that the fence had not, in fact, been set to a lethal level, seemingly explaining away his brush with death. However, in the Season 3 finale, "Through the Looking Glass," Mikhail is shot through the chest with a spear gun by Desmond and again seems to have been killed. Mikhail undergoes another miraculous recovery and swims out of the station where he then blows open a porthole, flooding the control room and killing Charlie.
The Others appear to operate on the assumption that cancer is impossible on the island, or at least within their own population ("One of Us"); Ben Linus appears deeply shocked when told he has a tumor on his spine.
The island does not appear to heal all people equally. Richard Alpert says in "The Brig" that Locke's spine healing itself is not a normal event, even by the island's standards; it is a sign of Locke being somehow "special". The effects of this specialness can extend to other people. After his spinal surgery, Ben is paralyzed for over a week, but regains the feeling in his legs immediately after coming into contact with Locke. He is able to walk (with the aid of a cane) only days afterward.
Aviation is apparently able to reach the Island in some way, however. In season 2's "LOCKDOWN" episode, a pallet drop of supplies is dropped on the Swan Station, presumably by a C-130 or some sort of prop-type cargo plane, although the producers have dropped hints that the pallets may not come from above at all. Naomi was also able to reach the island via helicopter with relative ease as well, considering that the Looking Glass jamming station was still in use during her flight. Furthermore, the original Henry Gale was able to land his balloon on the island in some manner as well.
Entering or leaving the Island itself is said to be extremely dangerous, especially if one has been exposed to a high amount of radiation or electromagnetism. Doing so under these circumstances can lead to one's consciousness traveling through time, eventually leading to one's death unless a "constant" (proposed by Faraday on Lost) can be found between the present and the destination time period. Whatever barrier there is between the Island and the rest of the world distorts time and is difficult to get through, producing a great amount of turbulence for planes, boats, or even submarines. If you are not on the bearing of 305, this can result in physical time travel, since Sayid, Desmond, and Lapidus went about a day in the future when they didn't go on the correct bearing. It appears that electronic signals and other non-living objects are also prone to do this, and they can go either in the past or the future.
The monster has been described by Lost producer Damon Lindelof as "one of the biggest secrets" of the mythology. It was introduced early on in the show. On the night after the crash, the survivors hear a loud, unidentifiable sound coming from the jungle and witness trees being torn down in the distance. The next morning, while discussing the sound the monster made, Rose commented that, "I keep thinking, there was something familiar about it." Jack, Kate, and Charlie saw the power of the monster up close when it ripped the pilot from the cockpit of the plane they crashed in and left the mangled body in a tree, all without being seen on-screen. In "Walkabout", Locke also had a direct encounter with the monster but was spared. When Michael later asked Locke if he had seen it, Locke lied and claimed that he had not. Locke later told Jack, "I looked into the eye of this island, and what I saw was beautiful."
In "Exodus, Part 1", Danielle referred to the monster as a "security system" whose purpose was to protect the island. Later in the episode, Locke's second encounter provided the first on-screen glimpse of the monster: a black mass of smoke accompanied by mechanical-like sounds. In "The 23rd Psalm" Charlie and Eko had a confrontation similar to Locke's. As Eko stared down the monster, the black smoke briefly flashed images of Eko's past. John Locke then stated that when he first saw the monster, it appeared as a "bright light" which he described as "beautiful," to which Eko replied, "That is not what I saw." In "The Cost of Living", the monster killed Eko by slamming him repeatedly against nearby trees and the ground. In another unseen appearance, the mechanical sounds of the monster can be heard during the episode "Exposé", right before Nikki is bitten by a "medusa spider", the same species as one of Arzt's research spiders, and in the episode "Special" when Michael is talking to his wife you can hear the monster for three seconds. In the episode "Left Behind", the monster appeared twice. It is unseen by the audience in the first encounter, when it released a series of bright flashes near Juliet. The monster appears on-screen during the second encounter, where it is revealed that it cannot penetrate the Others' sonic wave fence. Juliet tells Kate that the Others don't know what the Monster is, but they know it doesn't like their fence. When Locke holds Ben at gunpoint in "Confirmed Dead" he asks Ben, "What is the Monster?" and Ben, like Juliet, says that he doesn't know.
However, in the episode "The Shape of Things to Come", it becomes apparent that Ben knows more about the Monster than he has let on. After becoming enraged over the death of Alex, Ben disappears into a hidden room, which has an ancient stone door covered with hieroglyphs, only to emerge several minutes later covered in a dark ash like substance, telling the others they need to be as far away from the attacking mercenaries as possible. The Monster then suddenly arrives, and proceeds to attack and incapacitate all of the mercenaries. It slithers on the ground causing the Barracks to rumble and consumes Keamy's team, extending a hand-like tendril to draw back a man running from it. However, in the next episode it's revealed that the mercenaries survived albeit badly shaken. When questioned about an injured man, Keamy responds that he was, "thrown 50 feet into the air by a black pillar of smoke".
The monster later appears as a drawing in Cabin Fever. In a flashback, Richard Alpert comes to visit a five-year-old Locke in the early 1960s. Alpert becomes fascinated by a picture of the monster which Locke drew, asking Locke "Did you draw that, John?". Neither Alpert or Locke provide any further elaboration. In the picture, the monster appears to be swirling around an unidentified person.
The May 26, 2006 official Lost podcast claimed that viewers have seen the monster after "The 23rd Psalm" without realizing they were looking at it, which has led to fan speculation that the Monster actually is, or is at least responsible for, some of the manifestations that have appeared to the characters. In the March 21, 2008 official Lost podcast, Damon Lindelof said that manifestations of the Monster included Yemi, the Medusa Spider that bit Nikki, and some of Walt's appearances while he was not with the Survivors, although they were in more of a joking manner so they may have not been serious. Also, the producers have often hinted that the black cloud of smoke is not a monster in the traditional sense nor is it a cloud of nanobots.
In January 2007, producers Damon Lindelof and Carlton Cuse asked fans on Yahoo! Answers what they thought the monster was. They later picked their "favorite answer... not that's it's the right answer [sic]." The response they chose suggested that the monster was "originally a highly advanced security system designed to separate participants of the DHARMA experiments" and frighten them with smoke and loud noises to prevent them from wandering outside of their hatches. "However, the electromagnetic force of the island...mutated it - in the same sense that Desmond experienced time travel and can now see the future after [his] exposure) and made it malevolent and able to physically [interact with things]." The respondent also theorized that the monster could be "turned off" if the survivors found a control room for it. The producers restated that the answer could be "somewhat right, totally right - or completely off-base", but they thought it was "very cool and intriguing."
The Swan Station's Blast Door map makes several references to a "Cerebus" activity and also notes that this "Cerebus" prevents passage between certain stations, indicating the 'Security System' aspect of it may have gone down as early as 1984, which could well be the 'Incident' that Doctor Candle refers to during the Swan Stations' Orientation video. Notations on the Blast Door map seem to confirm the "Cerebus" patroling regions of the island that the Monster has been seen as well, hinting that the two may well be the same.
The numbers 4, 8, 15, 16, 23 and 42 appear throughout the series, both in sequence and individually. They were broadcast from the Island's radio transmitter, and it was this message that drew Rousseau's expedition there. Although she later changed the message after the deaths of the rest of her team, the numbers had also been heard by other people, eventually making their way to Hurley, who had used them to win a lottery before the crash. After those around him suffer a series of misfortunes, he begins to believe the numbers are cursed. In the episode "Numbers", it is revealed that Hurley heard the numbers from Leonard Sims, a patient at a mental hospital. Sims had received them from Sam Toomey, with whom he had served in the U.S. Navy, at "a listening post monitoring longwave transmissions over the Pacific" 16 years earlier. The numbers are continually prevalent throughout the entire show, as they are engraved on the hatch of the Swan station, appear on medicine bottles, and constitute a code that must be entered into the Swan station's terminal.
According to the DHARMA Orientation video in the Lost Experience, the Numbers represent the exponents of the Valenzetti Equation, which claims to accurately predict when humanity will be extinguished. The numbers also add up to 108, the time limit the survivers have to input the numbers in the hatch and "Save The World".
A large number of DHARMA workers were slaughtered by the Others at some point before the series began, hinted to be in 1992 during season 4, in a sequence known as "The Purge", as revealed in "The Man Behind the Curtain", although it is currently unknown whether or not there were any survivors. It has been confirmed in a podcast by the writers that Kelvin Inman was indeed a member of the DHARMA initiative who survived the purge, as was his partner Radzinsky who killed himself by gunshot before the crash of 815., assuming of course that Inman was telling Desmond the truth about Radzinsky.
The character Richard Alpert appears on several occasions, in different moments in time separated sometimes by decades within the series, and every time he has appeared so far, he seems to be always the same age. Whether this is due to Richard time traveling from circa 2004 (the time of the show), or the result of some supernatural aging process, is unknown.
For example: Sawyer converses with Jack's father in a bar before boarding the plane; Hurley's accountant buys him the box company that Locke had worked for; Hurley can be seen on a television in one of Jin's flashbacks; and Jack is asked to choose between performing operations on his future wife (whom he hadn't met yet) or Shannon's father (and Boone's stepfather).
The show's producers have always said that there was a reason characters appeared in each other's flashbacks. Damon Lindelof has stated that these are not "Easter eggs," but rather a larger part of the mythology of the series.
On the Island, numerous characters experience auditory and visual hallucination-like phenomena, including apparent visions and messages from deceased family members. Both Jack and Eko receive visitations from dead relatives whose bodies are present on the island. Similarly, Locke converses with the deceased Boone during a vision quest in "Further Instructions". Previously, he received a similar vision, directing him to the site of a crashed airplane, while Boone was still alive. In the episode "The Man Behind the Curtain", Ben sees his deceased mother on the island twice as a child, and this eventually leads him to join "the Others".
An image of Walt appears to Shannon on a number of occasions during Season Two, and is later seen by Sayid, just prior to Shannon's death. In "Man of Science, Man of Faith", a water-drenched Walt appears before Shannon, and whispers, incomprehensibly, something that sounds like reversed speech. Walt has been seen by Sayid, Shannon, and Locke.
Hurley experiences visions of Dave, an imaginary friend whom he had seen before while in a mental institution. Dave goads Hurley into briefly believing that the Island itself is his hallucination, and that he can only reawaken to his real life (in the mental institution) by leaping from a cliff.
Kate receives two visitations from her past: the seemingly channeled message from her deceased stepfather, spoken by Sawyer while in delirium; and later, an appearance of a black horse which she believes is the same one that enabled her escape from custody. The horse was seen by Sawyer as well, and both he and Kate touched it and concluded that it was real.
In a Missing Pieces episode, Jack's father Christian is shown interacting with Vincent and directing the dog to "wake Jack".
There has also been an occasion when a living person (apart from Walt) on the island was seen as a vision. A few days after they crashed. Boone sees a vision of Shannon being attacked by the "monster", leading him to try to rescue her; he fails and Shannon dies. He is shocked, however, when Locke tells him Shannon is alive and well. This particular vision though, was due to a hallucinogenic ointment made by Locke and smeared into a wound he gave Boone on the back of his head. Upon Boone's return, Locke exclaims that he "did not know it would make him see that," speaking of Shannon's death.
Sayid sees a cat that looks like one belonging to a woman whom Sayid had previously tortured, prior to the crash.
In the future, these visions seem to be capable of taking place off-island. The most recent example is in "The Beginning of the End"; Hurley, after leaving the island, has visions of his deceased friend Charlie, saying "they need you". These visions convince Hurley to resubmit himself to his old mental institution. The off-island vision occur again when Jack sees and hears his father sitting in a lobby chair at the hospital where he works in "Something Nice Back Home". Also, in the finale to season 4, Sayid finds Hurley by himself at a chessboard, and Hurley eventually reveals he was playing chess with Mr. Eko.