Multi-Doctor event

"Multi-Doctor Event" was a term used by the Twelfth Doctor to refer to incidents in which several incarnations of the Doctor interacted.

Clara Oswald, Alice Obiefune, and Gabby Gonzalez sought to prevent a Multi-Doctor Event by keeping the Tenth, Eleventh, and Twelfth Doctors from meeting each other when they were all near the same café in 1923 Paris. (COMIC: Four Doctors)

Multi-Doctor Events
The First Doctor was aware that "all" of his incarnations would be present at the funeral of Alistair Gordon Lethbridge-Stewart and would behave themselves, though some would argue at the wake. (PROSE: The Gift) Those known to have attended included the Second, Third, Sixth, Seventh, Ninth and Eleventh Doctors. (PROSE: Shroud of Sorrow)

The First Doctor once invited his first seven successors to join him for Christmas dinner. (PROSE: The Feast of Seven... Eight and Nine)

The Time Lords temporarily extracted the Second Doctor, followed by the First Doctor, from their respective time streams to assist the Third Doctor against Omega. The Second Doctor was summoned by Goth while returning to the Land of Fiction to recover his recorder. (PROSE: Future Imperfect) The First Doctor, however, was caught in a time eddy and so could only provide his advice. (TV: The Three Doctors)

After he accidentally awoke an army of Sea Devils who proceeded to attack a submarine in England, the Fourth Doctor unexpectedly came into contact with the Third Doctor, who was accompanied by Jo Grant. Adopting a new identity to protect the timelines, the Doctor helped his predecessor to defeat the Sea Devils, and made a quick exit before the Third Doctor could discover who he was. (COMIC: Under Pressure)

When the Second Doctor's TARDIS became trapped in a pocket dimension that disrupted the link to the TARDIS's interior dimensions and destabilised reality, the High Council gave the Fourth Doctor and Romana permission to go against the Laws of Time and establish a link between the Fourth and Second Doctor's TARDISes so that the Fourth Doctor and Romana could enter the Second Doctor's console room and bring the interior back into sync with the exterior. During this crisis the Second Doctor and his companions entered the console room while the Fourth was still in it, but the future Doctor and Romana hid on the other side of the console from the younger Doctor and his companions and carefully manoeuvred around the room to stay out of sight until the Second Doctor left again, at which point they returned to the future version of the ship. (PROSE: Heart of TARDIS)

Lord President Borusa used Time Scoops to bring the first five incarnations of the Doctor, as well as several of their companions, to the Death Zone on Gallifrey as part of his plot to gain Rassilon's gift of immortality. However, the Fourth Doctor and Romana II were caught in a time eddy and so failed to arrive. After Rassilon granted Borusa the gift of immortality by confining him into the stone of the Tomb of Rassilon, the Doctors and their companions returned to their respective times and places. (TV: The Five Doctors)

When the Second Doctor was captured by Joinson Dastari and his augmented Androgum associate Chessene, the Time Lords permitted the Sixth Doctor to rescue his past self, allowing him to travel to the space station where the younger Doctor had been captured so that he could trace his abductors. (TV: The Two Doctors)

During Bonjaxx's birthday celebration, the Seventh Doctor and Ace met a future incarnation of the Doctor, who came with his companion Ria. (COMIC: Party Animals)

During his quest to assemble the Key to Time with Ace and Bernice Summerfield, the Seventh Doctor encountered his sixth incarnation while he was fishing with Frobisher. Discussing what difference it would make if they had not left Gallifrey, the Seventh Doctor was unable to convince his previous incarnation of their importance to the cosmos, but acquired his sixth incarnation's cat brooch, a piece of the Key to Time. Following this, the Seventh Doctor went to 1963 to acquire another piece, the TARDIS Instruction Manual. While doing so, he found his first incarnation, whom he tripped up to save him from an Imperial Dalek, which he shoved into the path of an oncoming bus. The Seventh Doctor quickly took his leave, leaving his original incarnation oblivious both to the identity of his saviour and to the danger he was in. (COMIC: Time & Time Again)

According to one account, the Seventh Doctor travelled back to give the Hand of Omega to the First Doctor. (PROSE: Echoes of Future Past)

When the Sirens of Time manipulated the Fifth, Sixth and Seventh Doctors into changing history to give the Sirens more power, the Temperon drew the three Doctors together on Gallifrey after the Sirens had aided the Knights of Velyshaa in their attack on the planet, allowing the three Doctors to learn what had happened and take action to seal the Sirens away forever, apparently erasing these events for everyone but the three Doctors. (AUDIO: The Sirens of Time)

A malfunction in an ancient prototype TARDIS on a human colony drew the Fifth and Seventh Doctors to the planet at different times, with the same disruption preventing the Doctors from simply returning to their TARDISes and leaving until the Machine had been destroyed. During their encounter, the Seventh Doctor began to recall the incident with the Knights of Velyshaa before being cut off by the Fifth Doctor, who had yet to experience that event. The Seventh Doctor also remembered teaming up with his other twelve selves to save Gallifrey. (PROSE: Cold Fusion)

The Seventh Doctor met another incarnation who was known as Muldwych. Despite his concerns about the First Law of Time, the Doctor assisted Muldwych in defeating the Charrl. Shortly afterwards, the Seventh Doctor visited Muldwych and had tea with him. (PROSE: Birthright) Muldwych later attended the wedding of Bernice Summerfield and Jason Kane, giving the Seventh Doctor the book The Unformed Heart and two halves of a time ring to use as the wedding rings. (PROSE: Happy Endings)

When the Eighth Doctor lost his memory due to a trap set by the Master, Rassilon gave the Doctor subtle telepathic instructions so that he could still pilot the TARDIS. Under Rassilon's guidance, the Doctor visited all seven of his past selves at key points in their lives so that he could offer them advice and assistance. (PROSE: The Eight Doctors)

When the Sirens of Time attempted to escape their prison by diverting the path of a prototype TARDIS, Leela and Romana were able to prevent the crew succumbing to the Sirens' influence, but the captain of the proto-TARDIS subsequently killed himself and his crew to prevent them succumbing again. To ensure that the test flight of the proto-TARDIS still took place, Romana contacted Professor Bernice Summerfield for help, with Benny finding the Sixth, Seventh, Fourth, Eighth, Third and Fifth Doctors to act as substitute pilots while Romana served as the ship's captain. The First, Second and Tenth Doctors were also drawn to the temporal disruption, but departed to keep an eye out for potential side-effects rather than join their other selves. (AUDIO: Collision Course)

The Tenth Doctor accidentally came into contact with the Fifth Doctor when their iterations of the TARDIS colided, resulting in the Fifth Doctor appearing in his successor's' TARDIS control room. This caused a paradox which risked the creation of a black hole that would endanger the universe. However, the Tenth Doctor was able to quickly enact a solution, having remembered watching himself doing so from the perspective of his predecessor. Bidding farewell, the Fifth Doctor returned to his own time soon after. (TV: Time Crash)

At the end of his final reward just prior to his regeneration, the Tenth Doctor collaborated with his immediate successor to save Henry Gordon Jago and George Litefoot from the Gentlemen of the Dice. (AUDIO: The Jago & Litefoot Revival)

To stop the Creevix, the Eleventh Doctor sent messages to his previous selves. (AUDIO: The Time Machine) Via the TARDIS, he contacted the Sixth Doctor and Peri Brown to ask them to obtain an omniparadox from the Santa Maria on 12 October 1492, and store it in the TARDIS, (AUDIO: Trouble in Paradise) allowing him to escape from the Creevix. (AUDIO: The Time Machine) He sent a message to Susan Foreman via a radio DJ while she and the First Doctor were on Earth in October 1963. The message involved introducing Cedric Chivers to Bob Dylan. (AUDIO: Hunters of Earth) He contacted the Fourth Doctor and Romana whilst they were inside the Babblesphere, to make sure they didn't destroy it and sent it to the Stellaris Museum of Artificial Intelligence. (AUDIO: Babblesphere) Via the TARDIS Internal Communication System, he contacted the Eighth Doctor in London in 1935 to get him to clear up interference in the form of an alien invasion using the William Tell Overture to invade the Earth. (AUDIO: Enemy Aliens) Clearing the interference not only allowed the Fourth Doctor copy to lure the Creevix to 2013, it also allowed the Eleventh Doctor to send the messages to his other selves. (AUDIO: The Time Machine)

Using his psychic paper, he sent a message to the Second Doctor in 2724 to ensure he saved Sophie Topolovic's research on the Quiet Ones. (AUDIO: Shadow of Death) Using an Ovid sphere, he contacted the Fifth Doctor in England in the 1920s to ensure that he delivered the Ovid sphere back to the Ovids instead of destroying it. (AUDIO: Smoke and Mirrors) Via a recording on a telephone, he sent a message to the Third Doctor to ensure he saved the therocite and sent it to Professor Reynart. (AUDIO: Vengeance of the Stones) In the form of a distress beacon of the Howling Jupiter and a video message left in the control room of the wreck, he told the Tenth Doctor and Donna Noble to stop the Wraith Mining Cartel, by locating Professor Merrit Erskine, obtaining his research and using it to make sure the existence of slaughter crystals on the planet of Death's Deal was made known to galactic authorities. He also told them to ensure that Lyric Erskine survived. (AUDIO: Death's Deal) Using the Voice of Stone, he contacted the Seventh Doctor and Ace aboard the Obscura in the 49th century to make sure that they saved Captain OhOne. (AUDIO: Shockwave) Hijacking a giant television screen in New Vegas, he told the Ninth Doctor to save the life of Police Chief James McNeil. (AUDIO: Night of the Whisper) The omniparadox allowed the TARDIS to escape and rescue the Eleventh Doctor from the alternate future created by the Creevix timeline. (AUDIO: The Time Machine)

The Ovids, impressed with Tegan, shared their knowledge with humanity in the far future, giving the Eleventh Doctor the technology he needed to use the therocite, left behind by Reynart in his lab, which was now being used by Cedric, to destroy Cedric's time machine. The research on the Quiet Ones was used to create sub-pulsar transmissions, which were used to lure the Creevix into seeking out Cedric in 2013 after the copy of the Fourth Doctor inside the Babblesphere lured them there. The Bob Dylan music led to Cedric meeting his wife, and when the time came for him to use the time machine to complete the final step that would ensure the Creevix timeline, he hesitated, giving the Eleventh Doctor the time he needed to stop the Creevix. Lyric Erskine was the mother of Guy Taylor, the Time Agent that the Creevix erased from existence in order for their plan to succeed, and her survival led to her meeting Captain OhOne, who was Taylor's father, and the pair conceived Taylor on their second honeymoon at the Memorial Hotel, founded by Mayor James McNeil. Taylor's restoration and arrival in 2013 was the final piece in erasing the Creevix timeline. (AUDIO: The Time Machine)

After Clara Oswald was abducted by Adam Mitchell, former companion of the Ninth Doctor, the Eleventh Doctor put a plan into action, tracking Adam to his fortress where he had allied with. The Doctor then summoned his ten predecessors, who had all lost their companions to Adam. With the assistance of Frobisher, the Doctors were able to set their companions free. When the Master revealed his intent to destroy the universe, Adam turned back and stopped him at the cost of his life. The Doctors and their companions returned to their respective times, but not before overlooking a memorial in honour of Adam's sacrifice. (COMIC: The Choice, Endgame)

When the War Doctor prepared to use the Moment to end the Last Great Time War by destroying the Time Lords and the Daleks on Gallifrey, the sentient weapon brought him as well as the Eleventh Doctor from the Under Gallery, into contact with the Tenth Doctor in Elizabethan England, where a Zygon incursion had been uncovered. After the three Doctors arranged a ceasefire between the Zygons and humanity in the 21st century, the War Doctor returned to the barn accompanied by his future selves, who had been let through the time lock. When Clara urged the Doctors to find another way to end the war, they got the idea to transport Gallifrey into a pocket universe on the last day of the Time War. To do so required the work of "all thirteen" of the Doctor's incarnations, up to the Twelfth Doctor. Following this, the Eleventh Doctor returned to the Under Gallery where, after seeing off his predecessors, made contact with the Curator, an incarnation from his future. He then had a dream in which he stood alongside his predecessors, all looking up at their home planet. (TV: The Day of the Doctor)

Shortly following his regeneration, the Twelfth Doctor made a brief indirect contact with his immediate predecessor when he listened in on a conversation on the phone between Clara and the Eleventh Doctor. The Eleventh Doctor, just prior to completing his regeneration following the Siege of Trenzalore, had made a call to the future to convince Clara to stay with his successor. (TV: Deep Breath)

The Twelfth Doctor recalled to Clara that his first four incarnations had attempted to form a band, only for it to fall apart due to creative differences. (COMIC: Day of the Tune)

Refusing to change despite being mortally wounded by the Cybermen, the Twelfth Doctor was taken by the TARDIS to Antarctica in 1986, where he came into contact with the First Doctor. (TV: The Doctor Falls) The First Doctor, who was nearing his own regeneration, likewise was hesitant to change, and his contact with his successor caused a timeline error which resulted in the appearance of Captain Archibald Hamish Lethbridge-Stewart from World War I, pursued by a glass avatar of the Testimony. After uncovering the nature of the Testimony, as well as changing history so the Captain did not die just prior to the Christmas truce, the two Doctors took their leave of each other, having been convinced to face their respective regenerations. (TV: Twice Upon a Time)

The Thirteenth Doctor visited the Fourth Doctor whilst he was trapped in the pocket dimension controlled by the Scratchman, to give him a reminder of what he stood for and what he had to be in order to encourage him to hold on to his true identity against the Scratchman's power. Once her past self, Sarah and Harry were back on Earth, the Thirteenth Doctor visited the Fourth directly to muse on how important it was that they never give up on being the Doctor. (PROSE: Scratchman)

Effects
Multi-Doctor events are normally forgotten by all except for the most recent incarnation involved. This was said to be as a result of each Doctor's timeline becoming unsynchronised when such an event occurred. Only incarnations of the Doctor who directly interacted during the event were affected. For instance, the Eleventh Doctor came away from teaming up with his previous incarnations to save Gallifrey with his memories of the event fully intact, despite the fact he was unknowingly being aided by his immediate successor. (TV: The Day of the Doctor)

Earlier Doctor's may still retain some recollection of specific happenings which occurred during the event. The Tenth Doctor was aware that he had married Elizabeth I, (TV: The End of Time), despite his Eleventh and War incarnations being present at the ceremony. (TV: The Day of the Doctor)

The Seventh Doctor, however, was able to recall teaming up with his future incarnations to save Gallifrey. (AUDIO: Cold Fusion)