Reconnaissance scout

The reconnaissance scouts, once referred to a "recon scout Daleks" by the Doctor or shortened to "recon scouts" for brevity, were specialised Daleks created by the early Dalek Empire when it began its conquests.

Nature
The reconnaissance scouts were tasked with doing reconnaissance work on alien planets in preparation for a Dalek invasion. Once a reconnaissance scout had scoped out a suitable planet, it would report back to the Dalek Fleet, summoning the invasion force.

Having been "especially advanced" from the "basic Dalek", the Dalek mutants designated as reconnaissance scouts had special abilities. They could possess other lifeforms, like humans, by sticking to the back, piercing the skin and using their tentacles to integrate themselves into the central nervous system of the creature, forming a mental link so to control their hosts. They were also capable of remotely disrupting circuitry, as experienced by the Doctor's TARDIS' circuitry and disabling their sonic screwdriver. (TV: Resolution)

The augmented mutants could also use ultraviolet light to teleport; (TV: Revolution of the Daleks) if cut up and divided into pieces, only one of the pieces had to be exposed to ultraviolet light for the Dalek to be able to literally pull itself back together and fuse back into one being. (TV: Resolution) At least after its resurrection, which had admittedly corrupted and mutated part of its DNA, one recon scout Dalek displayed the ability to fatally electrocute its human host even as it teleported. (TV: Revolution of the Daleks)

A day to come
Through the extrapolations of the Matrix, the Time War-era Time Lords foresaw the encounters with the Reconnaissance Dalek in the Doctor's personal future. Though they regarded all future events they saw as merely theoretical, it was recorded in the Dalek Combat Training Manual in a chapter for section leaders. They attributed the "remarkable" feat of the Dalek having initially been defeated by primitive humans to it being unprepared for the overwhelming opposition that it faced, anticipating that they would not be so lucky were they to encounter one. Regarding the 2021 Dalek civil war, it came much to the concern of the Time Lords that a single Dalek was able to create a whole new mutant strain of the Dalek race without the advanced skills of Davros, the Dalek Emperor or the Cult of Skaro. As such, they began research into the genetic make-up of the Reconnaissance Daleks to further understand the extent of their abilities. (PROSE: Dalek Combat Training Manual)

The Reconnaissance Dalek
One such Dalek arrived on 9th century Earth. It was defeated by an army of humans on British soil in the Battle of Hope Valley. The mutant was divided into three pieces by the Three Custodians, while its casing was destroyed. Some parts of the casing remained, and the third Custodian did not complete his journey to the burial site in Yorkshire.

This part, recovered by archaeologists in Sheffield, was exposed to ultraviolet light and the energy restored it. The mutant was able to possess Lin and forced her to rebuild its casing using what was left from the 9th century and Earth supplies from a farm owned by a man it killed named Dinkle. (TV: Resolution) During the Recon Scout Incident, (PROSE: Dalek Combat Training Manual) the Dalek continued its mission in preparing Earth for an invasion from the Dalek Fleet.

The Dalek was finally defeated when the Thirteenth Doctor jettisoned it into a supernova. (TV: Resolution) However, it was resurrected from traces of its DNA by Leo Rugazzi acting on the payroll of Jack Robertson, and, after taking control of it and highjacking Robertson's financial empire, the Reconnaissance Dalek decided to create a new race of Daleks from its own DNA template. Accordingly, the new Daleks all shared the original recon scout's ability to teleport using ultraviolet light. These recon-scout-clones were, however, all destroyed by the Dalek Death Squad in the 2021 Dalek civil war. (TV: Revolution of the Daleks)

Behind the scenes
James Johnson rendered a Time War-era Reconnaissance Dalek model which was featured on the cover of Gallifrey: War Room 1: Allegiance. Ahead of release, Johnson released a closer look at his designs, also clarifying that the accompanying text wasn't in any way official, and that he added it "just for fun". These bronze-type Daleks were equipped with Focusing Emitters and Deflector Globes. "Reconnaissance Daleks were distinguished by their red domes during the Last Great Time War. These Daleks were battle proven mutants that had survived previous campaigns and were programmed in the art of guerilla warfare, espionage and reconnaissance. They were often deployed in smaller groups behind enemy lines on multiple fronts and varying timelines."

- James Johnson