Tissue Compression Eliminator

The Tissue Compression Eliminator (or TCE), also called a decompression eliminator (AUDIO: The Evil One) or simply the Compressor, (TV: The King's Demons) was a trademark weapon of the Master. He admitted that he wasn't sure about the name, if it eliminated victims through tissue compression or if it, in fact, eliminated tissue compression. (AUDIO: The Two Masters)

Function
The Fourth Doctor once described the method by which the Master killed as "matter condensation." (TV: The Deadly Assassin) As its name suggested, the TCE killed by drastically compressing the bodies of its targets to the point where life functions ceased, firing a modulated beam of gravitons and Pym particles. (PROSE: The Quantum Archangel) Eventually, the victims were no longer visible after the exposure, but the Master liked to leave the shrunken doll-like corpses of his victims as a calling-card for the Doctor to discover in places the Master anticipated the Doctor would look. (TV: The Deadly Assassin, The Timeless Children)

The TCE was equally capable of shrinking inorganic tissue: victims' clothes were also shrunk. On one occasion, the Master demonstrated the weapon by shrinking empty space-suits to intimidate Peri when he took her captive on Sarn to ensure she co-operated with him. (TV: Planet of Fire)

According to Sally Armstrong, it usually compressed people by a factor of 10. (AUDIO: Eyes of the Master) gave Sally a TCE which also acted as a communicator. (AUDIO: The Reviled)

The Seventh Doctor kept one of the Master's TCEs, using the device to shrink Death's Head to regular size. (COMIC: The Crossroads of Time) He later used the device (adapted) to electrocute Head, knocking him out. (COMIC: The Incomplete Death's Head)

Use against UNIT
used the TCE to kill Goodge to infiltrate a radio telescope for the Nestene Consciousness. (TV: Terror of the Autons)

He once materialised his TARDIS within UNIT HQ and attacked the Third Doctor. In the brawl, the Doctor took the TCE and the Master fled.

The Doctor threatened the Eighth Doctor with the TCE, hoping he would hand over the TARDIS. Ultimately, he decided against it and handed the device to his future self. (PROSE: The Eight Doctors)

The Master's disfigurement
According to one account, before his disfigurement, the decided to "spice things up a bit" by using a staser instead of the TCE. After swapping bodies with, (AUDIO: The Two Masters) he returned to using the TCE. (TV: The Deadly Assassin)

Another account, however, suggested that the same Master who had been fond of using the TCE in his plots against the Third Doctor was the one who had become disfigured, and that, in fact, it was the device which caused his injuries. Specifically, Susan Foreman, after psychically assaulting the Master, stole his TCE and intended to use it to destroy the matter transmuter the Master had stolen. With the crazed renegade refusing to let go of the transmuter, she fired the TCE at the machine while he was still holding it, and the interaction of the two advanced matter-manipulation device tore apart the Master's body, also preventing regeneration. (PROSE: Legacy of the Daleks)

Having survived as a grotesque living corpse, the Master later used his TCE to kill a camera technician on Gallifrey, which alerted the Fourth Doctor to his presence. (TV: The Deadly Assassin)

Use in Tremas's body and beyond
The Master used it to kill several humans and Logopolitans in 1981. (TV: Logopolis)

The Fifth Doctor was able to use the TCE to sabotage 's TARDIS. (TV: The King's Demons)

later attempted to improve the design of his weapon, but a laboratory accident resulted in the laboratory and him both being reduced in size instead. This did not appear to harm him. (TV: Planet of Fire)

On another occasion the Master used the TCE against a velociraptor revived by the fountain of youth. However, it landed right back in the fountain, re-emerging unharmed but miniscule in size, making a comical sight. (PROSE: A Town Called Eternity)

The Sixth Doctor stole and used it to threaten and ; later Peri Brown did the same. (TV: The Mark of the Rani)

Izzy Sinclair was shrunk after being shot with a TCE without being killed outright by 's disciple Sato Katsura. She was later able to use the weapon to reverse the process. (COMIC: The Glorious Dead) also gave one to Sally Armstrong. (AUDIO: Eyes of the Master, The Reviled)

The Master used a TCE, or a similar device against Strax. (WC: Strax Saves the Day)

The Seventh Doctor's use
During his first encounter with the artificially-enlarged mechanoid freelance peacekeeping agent Death's Head, the Seventh Doctor used a TCE (which he happened to have on him) to defend himself against the mercenary. Death's Head was not injured, but found himself returned to his original size (that of a normal humanoid), which he retained for the rest of his career. (COMIC: The Crossroads of Time)

The Seventh Doctor also used a modified TCE to shock and incapacitate Death's Head (to prevent him from killing his future self and wipe his memory) during Bonjaxx's birthday party on Maruthea, knowing it had worked on him before. (COMIC: The Incomplete Death's Head)

Abandon by the Master
By the start of the Last Great Time War, (AUDIO: The Devil You Know, The Missing Link, The Heavenly Paradigm) the Master began using a laser screwdriver, of his own design, in lieu of the TCE. (TV: The Sound of Drums)

The TCE was, on the other hand, used by the parasitic being Es'Cartrss of the Tactire through a simulated reality in the Matrix of the Doctor's TARDIS; Es'Cartrss was posing as a version of the Meta-Crisis Doctor who had become the Valeyard and adopted the Master's beard and demeanour in the process. (COMIC: The Forgotten)

As, the renegade began using a new device that worked as a vaporising energy weapon, a camera, or even a time stop, (TV: Dark Water) although she also kept a TCE device disguised as her onix hat pin, retaining the four petals over a glowing sphere. (PROSE: Lords and Masters) She used the TCE to miniaturise the board of a boarding school in Scotland, so she could "have them in [her] pocket" to keep her position as headmistress. (AUDIO: Brimstone and Terror)

By the time she met her final end on a Mondasian colony ship, Missy's go-to gizmo was a sonic umbrella. (TV: The Doctor Falls)

A return to the "classics"
Feeling that tissue compression was "a classic", the Master's later incarnation acquired a new and improved Tissue Compression Eliminator, which now resembled an antique lighter. (TV: Spyfall) It could also work as a communication device. (TV: The Timeless Children) In order to steal his identity, the Master turned this TCE onto O, an athlete on his way to his first day to work as a spy for MI6. Deciding that it was good to "keep a backup of one's work," he Master kept what appeared to be the original O in a matchbox for years, eventually showing him to the Thirteenth Doctor to support his story. Later on, after pursuing the Doctor to 1834, he shrunk three people with the TCE, which he mockingly introduced to the audience of a science fair as "the Incredible Shrinking Device". (TV: Spyfall)

After reuniting with the Doctor on the Planet of the Boundary, the Master threatened the Doctor's friends with the device to force her to return to Gallifrey with him. The Master later threatened the Doctor with the TCE when she argued with him. After Ashad stated that the Cyberium would never leave him while he was still alive, the Master used the TCE to kill the Lone Cyberman, releasing the Cyberium. However, the death particle was not detonated by Ashad's death as the Master had hoped and was instead shrunk with him. (TV: The Timeless Children)

Behind the scenes
According to the short story TARDIS Stolen!, which dealt with the First Doctor's departure from Gallifrey in a comedic register and is not considered a valid source on this Wiki, the Master was, at the time of the Doctor's flight, selling "extremely lifelike dolls" in the Capitol for a tidy profit, suggesting that he had already invented the TCE before his departure from Gallifrey and officially becoming a renegade.