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.
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)
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. It 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)