Doom's vortex manipulator

Doom, an assassin who worked for the Lesser Order of Oberon, owned a vortex manipulator.

Abilities
Her employers, the Lesser Order of Oberon, transmitted a large number of coordinates to her vortex manipulator per day. Every hour, she could select one of those sets of coordinates at her discretion and travel there. (WC: Meet Doom - the Universe's Greatest Assassin!, etc.) It could also be used to check her life signs. (PROSE: Hour One)

The vortex manipulator had an in-built clock, (WC: Meet Doom - the Universe's Greatest Assassin!, COMIC: Target Selected, etc.) which could count down either the time until the end of a mission - (COMIC: Target Selected, etc.) at the end of which it would reactivate, deducting funds from either the client's account or from her wages, as with all assassins hired by the Lesser Order (PROSE: Hour One, etc.) - or a full countdown of Doom's remaining 24 hours to find the Doctor. (WC: Meet Doom - the Universe's Greatest Assassin!, The universe's greatest assassin has just 24 hours to escape Death and find the Doctor - where will Doom's Day take her next?)

This clock could display as either a digital clock (WC: Meet Doom - the Universe's Greatest Assassin!, COMIC: Target Selected, etc.) or an analogue clock, (WC: The universe's greatest assassin has just 24 hours to escape Death and find the Doctor - where will Doom's Day take her next?) and could be projected vertically in a pink hologram, in either format. (WC: Meet Doom - the Universe's Greatest Assassin!, The universe's greatest assassin has just 24 hours to escape Death and find the Doctor - where will Doom's Day take her next?)At the end of a mission, the manipulator would "[snatch Doom] away into the vortex", with a split-second between missions, and she would be given a number of assignments located "anywhere in time and space", with her having a moment to choose her next mission. (PROSE: Hour One, etc.) The manipulator could also transport objects with her. (COMIC: High Noon in Hollywood, The Horn of a Dilemma)

Mission on New Venice
During Doom's mission on New Venice, she used her vortex manipulator to check her life signs, finding that they were "not good", and that she had 24 hours to live. During a call with Terri, part of the Lesser Order of Oberon, she checked the readout on her vortex manipulator, reporting these statistics, leading to Terri deciding to work on an early Death-In-Service Report. Doom pleaded with Terri, stating that she wasn't dead yet, and again reiterating what her vortex manipulator said, with her knowing that she'd need to find the Doctor again, after her earlier encounter with him.

At the end of her mission, she decided that, as the Doctor could be anywhere in time and space, so could she, and that so long as she was on the rota, she'd have 24 hours before she was gone, equating to 24 chances to find the Doctor. She's previously been successful in overthrowing the Daedalus Conspiracy, sealing the Mandeville Dimension, and saving Princess Agatha from her seven deadly husbands, leading to her feeling confident in her 24 chances, as she'd only had a single chance at said earlier missions.

Death began to come for Doom, leading to her pleading for Terri to send her a new target. Terri obliged, sending her a list, which included "The Alderton Array", "Madrigal’s Escalation", and "The Stormcage Containment Facility". Doom chose the last of these, as she felt she'd find either the Doctor, or someone who knew them very well, there. Doom then activated her vortex manipulator, flinging her into the vortex. (PROSE: Hour One)

Use at the Stormcage Containment Facility
Upon arriving at Stormcage Containment Facility, Doom sorted out her target there. (COMIC: Target Selected) At some point, she reflected that she had 23 hours to go, and that she needed to find the Doctor. (WC: The universe's greatest assassin has just 24 hours to escape Death and find the Doctor - where will Doom's Day take her next?)

She later entered the cage which contained River Song, River recognising her as "cold-blooded killer" like herself. Doom told River that she was after someone close to her, with River advising that she takes the mission on New Calamino at the waxworks museum, as he was one of the exhibits. Doom thanked her for her help, and found that her time there was up, moving on to her next mission. (COMIC: Target Selected)

Use at the waxworks museum, New Calamino
After being advised to go there by River, (COMIC: Target Selected) Doom arrived at the waxworks museum in New Calamino, posing as one of the exhibits alongside the Sixth Doctor. After sorting out the situation there, Doom found that he was the wrong Doctor, and that she was out of time on that mission, moving on to her next one. (COMIC: The Plastic Population)

Use in 1930s Hollywood
Arriving in 1930s Hollywood, Doom found the place overrun with Cybermen. She completed her mission and found a chest of treasure and a model of a sabre-toothed tiger, (COMIC: High Noon in Hollywood) both of which she brought with her (COMIC: The Horn of a Dilemma) after seeing that her time was up there. (COMIC: High Noon in Hollywood)

Use at a renaissance fair
Arriving at her next mission in a renaissance fair, Doom completed her mission of killing the idea of the unicorn to save them from being hunted to extinction, making use of the treasure she took with her (COMIC: The Horn of a Dilemma) from 1930s Hollywood. (COMIC: High Noon in Hollywood) Jo Grant told her that she had a friend who could help, but Doom declined, as she could tell her time there was nearly up from looking at her manipulator. She ran off in search of the Doctor as behind her, Jo entered the Doctor's TARDIS. (COMIC: The Horn of a Dilemma)