CyberIsomorph

CyberIsomorph, or simply Isomorph, was the term an ArcHivist assigned to a Cyberman subspecies, a variant of CyberNeomorph that was stranded, or isolated, in the late 20th century. (AUDIO: The Ultimate Cybermen)

Vulnerabilities
The Isomorphs inherited both the resilence and weaknesses of the earlier Neomorphs and the preceeding Cyberman subspecies. While 20th century human firearms inflicted little to no damage upon them, the Cybermen remained vulnerable to gold. Indeed, Lady Peinforte and Ace, using a bow with gold-tipped arrows and a slingshot with gold coins respectively, were able to destroy these Cybermen with a single hit to their chest panels. However, the Cyber-Leader proved more resilient as it survived being struck by a coin, which it dislodged from its chest unit, only to be finally killed when Richard Maynarde thrust an arrow into its chest. (TV: Silver Nemesis)

Origin
In an attempt to avert their future defeat, CyberNeomorphs based on Telos used a stolen time vessel to travel back centuries in the past to Earth in 1985, where they intended to destroy the planet in order to prevent the destruction of their original homeworld, Mondas, which occured in the following year. Ultimately, this plot was foiled by the Sixth Doctor. (TV: Attack of the Cybermen) However, a group of Neomorphs remained stranded in the late 20th century. (AUDIO: The Ultimate Cybermen)

Operations
In November 1988, a scouting party of Cybermen was sent to Earth in search of a statue made of validium called Nemesis, a Time Lord weapon. The Cybermen met Lady Peinforte, who brought many of their number down with gold-tipped arrows. The Leader apparently forced the Seventh Doctor to surrender the Nemesis. Their force was destroyed by Nemesis as the Doctor had instructed. (TV: Silver Nemesis)

Legacy
UNIT collected the body of one of the Cybermen that were killed by Lady Peinforte and stored it at the Underbase. (COMIC: The Age of Ice)

Behind the scenes
"Isomorph" was coined by David Banks to distinguish the Cybermen seen in Silver Nemesis, who sported several cosmetic differences from the earlier "Neomorphs", as well as explaining why that story had them present in the 20th century, linking to the Neomorphs' earlier use of time travel in Attack of the Cybermen.