The Master's regeneration cycles

The Master had several regeneration cycles making up their many lives, as well as some regenerations achieved through other means.

Original regeneration cycle
Their original life cycle, lasting twelve regenerations following the Master's first incarnation, was used up at a faster rate than most Time Lords. (TV: The Deadly Assassin)

Accelerated use
The Master used his original regeneration cycle at an accelerated rate compared to other Time Lords. (TV: The Deadly Assassin) Various accounts offered explanations for this.

The Fourth Doctor believed that the accelerated use came from the Master living a high pressure criminal life, with regenerations used as disguises. (PROSE: Doctor Who and the Deadly Assassin)

Magnus was notably frivolous with his regenerations. (COMIC: Flashback, PROSE: Invasion of the Cat-People)

claimed that he'd wasted all of his lives because of the Doctor. (TV: Doctor Who) An account of this occurred in Koschei's meeting with the Second Doctor, which ended in Koschei expending several lives to escape an event horizon. (PROSE: The Dark Path)

A Brief History of Time Lords believed that the accelerated use of regenerations came from living a life "more rackety than the Doctor's". (PROSE: A Brief History of Time Lords)

First incarnation
By one account, Koschei was the Master's first incarnation, who received the regeneration cycle when he got the Rassilon Imprimatur after graduating from Prydonian Academy. (PROSE: Divided Loyalties)

In an alternate timeline, a young Master who had yet to leave Gallifrey was one of several incarnations who gathered on Kiamet. (AUDIO: Masterful) Missy remembered that the Master had left Gallifrey by the time of their first regeneration. (PROSE: Dismemberment)

CIA File No. 197,648,200/7A indicated that the Master's first incarnation lived on Gallifrey before the Master became a Renegade Time Lord. After attending the Prydonian Academy, the Master began conducting field work studies of historical interplay and temporal structure through use of intervention, during which he regenerated. (PROSE: CIA File Extracts)

Second incarnation
After the Master regenerated for the first time, by Missy's memory, his new incarnation found himself at the Scoundrels Club during the Great Fire of London. Becoming a member of the club so that he could recover from the regeneration in comfort, the Master organised fireworks on the roof to celebrate the occasion. He would later go on to visit the Scoundrels Club after each regeneration to recover as a tradition. (PROSE: Dismemberment)

CIA File No. 197,648,200/7A indicated that the Master's second incarnation lived on Gallifrey before the Master became a Renegade Time Lord, regenerating during his time conducting field work studies of historical interplay and temporal structure through use of intervention. (PROSE: CIA File Extracts)

Third incarnation
CIA File No. 197,648,200/7A indicated that the Master's third incarnation lived on Gallifrey before the Master became a Renegade Time Lord, regenerating during his time conducting field work studies of historical interplay and temporal structure through use of intervention. (PROSE: CIA File Extracts)

Fourth Doctor was unsure if an incarnation of the Master he met was on his second or third "regeneration". (AUDIO: Blood of the Time Lords)

Fourth incarnation
CIA File No. 197,648,200/7A indicated that the Master's fourth incarnation lived on Gallifrey before the Master became a Renegade Time Lord, regenerating during his time conducting field work studies of historical interplay and temporal structure through use of intervention. (PROSE: CIA File Extracts)

Fourth Doctor was unsure if an incarnation of the Master he met was on his second or third "regeneration". (AUDIO: Blood of the Time Lords)

Fifth incarnation
CIA File No. 197,648,200/7A indicated that the Fifth Master was responsible for the Prydonian Academy Revolution, and was mortally wounded by Arkendo when he fled Gallifrey to become a renegade. (PROSE: CIA File Extracts)

Sixth incarnation
CIA File No. 197,648,200/7A indicated that the Master's sixth incarnation was a renegade known as the Monk. After meeting the First Doctor in 1066, this incarnation was killed by being trapped in a shrinking TARDIS. (PROSE: CIA File Extracts)

Seventh incarnation
CIA File No. 197,648,200/7A indicated the Master's sixth incarnation regenerated into an identical-looking seventh incarnation also known as the Monk, who faced the First Doctor a second time. This incarnation discovered Merast, the Master's secret base. This incarnation was killed by the Daleks following his role in the Time Destructor Incident. (PROSE: CIA File Extracts)

Eighth incarnation
CIA File No. 197,648,200/7A indicated that the Master's eighth incarnation was the first to call himself "the Master". Once more with a bearded face like that in which he would face the Third Doctor, the Master began enacting various plans of universal domination, some of which succeeded and some of which ended in failure, sometimes due to Celestial Intervention Agency intervention. He suffered a setback which resulted in his regeneration. (PROSE: CIA File Extracts)

Ninth incarnation
CIA File No. 197,648,200/7A indicated that the Master's ninth incarnation, who resembled the thirteenth Master, enacted various plans of universal domination, some of which succeeded and some of which ended in failure, sometimes due to Celestial Intervention Agency intervention. He suffered a setback which resulted in his regeneration. (PROSE: CIA File Extracts)

Tenth incarnation
CIA File No. 197,648,200/7A indicated that the Master's tenth incarnation, who resembled the thirteenth Master, enacted various plans of universal domination, some of which succeeded and some of which ended in failure, sometimes due to Celestial Intervention Agency intervention. He suffered a setback which resulted in his regeneration. (PROSE: CIA File Extracts)

Eleventh incarnation
CIA File No. 197,648,200/7A indicated that the Master's eleventh incarnation, who resembled the thirteenth Master, enacted various plans of universal domination, some of which succeeded and some of which ended in failure, sometimes due to Celestial Intervention Agency intervention. He suffered a setback which resulted in his regeneration. (PROSE: CIA File Extracts)

Twelfth incarnation
CIA File No. 197,648,200/7A indicated that the Master's twelfth incarnation, who resembled the thirteenth Master, enacted various plans of universal domination, some of which succeeded and some of which ended in failure, sometimes due to Celestial Intervention Agency intervention. He suffered a setback which resulted in his regeneration. (PROSE: CIA File Extracts)

Thirteenth incarnation
According to the CIA File No. 197,648,200/7A, with many plans unfolding from the activities of his past few incarnations, including several connections formed for future alliances, the Master's thirteenth and final incarnation set his sights on Earth. This was the body in which he faced the Third Doctor. After being wounded during the Second Dalek War, the Master's handsome features began to decay, leading to the thirteenth incarnation surviving as the Decayed Master. (PROSE: CIA File Extracts)

The Decayed Master once claimed that he was "nearing the end of [his] twelfth regeneration". (TV: The Keeper of Traken)

Attempted fourteenth incarnation
By some accounts, the Decayed Master was created when the Master attempted a thirteenth regeneration beyond their allotted twelve. (PROSE: Divided Loyalties, Meet Missy!, The Doctor vs the Master)

Incarnations of ambiguous numbering
Several accounts indicated the incarnation of the Master who faced the Third Doctor was capable of regeneration, indicating him to not be the thirteenth incarnation. (PROSE: Legacy of the Daleks, AUDIO: Sympathy for the Devil, COMIC: Doorway to Hell)

Post-mortem & legacy
When the "Tremas" Master was stripped of his Trakenite body by the Time Lords, and after his plot to steal the Fifth Doctor's regenerations failed, he found himself confronting mental projections of all his past incarnations, and was able to steal a bit of life energy from each of them, allowing him to regenerate back into his Trakenite body. (PROSE: The Velvet Dark)

The Master would spend considerable time attempting to gain a new regeneration cycle to continue surviving, sometimes mentioning their original regenerative cycle. (PROSE: Cold Fusion, The Quantum Archangel, et al.)

Non-cyclical regenerations
On Gallifrey, the Decayed Master tried to regenerate. (TV: The Deadly Assassin)

Tzun-granted life cycle
The Tzun gave the Tremas Master a new regeneration cycle, which resulted in a regneration which created a new Gallifreyan Master. (PROSE: First Frontier)

The Master acquired the physiology of a Deathworm Morphant to survive his execution by the Daleks. (AUDIO: Mastermind, TV: Doctor Who) After using this form to possess a human body, Bruce Gerhardt, understood that this body was beginning to decay and so tried to use the Eye of Harmony to steal the Eighth Doctor's remaining regenerations to heal himself, but his plans were foiled when Grace Holloway sent the TARDIS' into a temporal orbit. The Master ended up falling into the Eye of Harmony, (TV: Doctor Who) but eventually escaped the TARDIS, finding that his human body had been "energised" by the Eye. (AUDIO: Day of the Master)

Resurrected regeneration cycle
By some accounts, the Master's resurrection led to them being granted a new regeneration cycle, with the Decayed Master regenerating into the Reborn Master. (AUDIO: Day of the Master)

The War Master, after escaping the Last Great Time War, was forced to regenerate into the Saxon Master after being shot by Chantho. (TV: Utopia)

Following the Year That Never Was, the Saxon Master was himself shot by Lucy Saxon but refused to regenerate, choosing to die rather than live with the Tenth Doctor, who proceeded to burn the Master's body. (TV: Last of the Time Lords) However, the Master had made arrangements for the Disciples of Saxon to resurrect him using salvaged biometrical signatures. This process was interrupted by Lucy Saxon, resulting in the resurrected Saxon Master burning up his own life force. He was embroiled in the Ultimate Sanction, which ended with him returning to Gallifrey at the end of the Time War. (TV: The End of Time)

As the Twelfth Doctor learnt, the Time Lords had cured the Master's "little condition" before "kicking" him off Gallifrey. The Master ended up trapped on a Mondasian colony ship where he found his future self, Missy, with the Doctor. Refusing to stand with the Doctor, the Master used his laser screwdriver to shoot Missy on full blast, preventing her from regenerating, but not before she inflicted a mortal wound by stabbing him, forcing him to regenerate into her. (TV: The Doctor Falls)

Elysian field regeneration cycle
By one account, Missy used an Elysian field to obtain a new regeneration cycle to survive her death. This resulted in the creation of a new incarnation, the Lumiat, who sought to do good. However, the Lumiat was shot by a younger version of Missy after attempting to interfere in the schemes of her younger self. Forced to regenerate, the dying Lumiat was dumped by Missy on a random planet. (AUDIO: The Lumiat)

Following Missy, (PROSE: The Wonderful Doctor of Oz) the Spy Master repeatedly menaced the Thirteenth Doctor and ultimately enacted a plot to take over her body and identity by subjecting her to a forced regeneration. This was initially successful, with the Doctor's body changing to reflect the Master's form, but was undone by Yasmin Khan using regeneration energy taken from the CyberMasters. This forced the Master back to his own body, which began to fail as a result of his actions. (TV: The Power of the Doctor)

Behind the scenes
to be added