Rusty

Rusty is a Dalek which first appears in Doctor Who Series 8 episode 2 "Into The Dalek". Some time later, Rusty reappears during an incursion between the Doctor, Alyssa and Clara, and the Daleks, saving the three from imminent extermination. Rusty informs the Doctor of an impending Dalek invasion of a Level 5 planet, similar to Earth, and joins them in saving the planet from the Daleks. Rusty appears at this time with notable upgrades in firepower and defenses purposed for battle superiority against his own kind. Rusty reappears in later episodes, assisting the Doctor and his companions in fighting Daleks and Cybermen.

First Appearance
"Rusty", named so by the Doctor due to its heavily damaged appearance, is captured and held by rebels aboard the starship Aristotle. Rusty appeared to have suffered from a unidentified condition causing him to become "good" through his desires to exterminate his own kind. Utilizing a miniaturizing device, the Doctor, Clara, Alyssa and a team from the Aristotle enter the Dalek "Rusty" through its eyestalk to find out what has gone wrong with him. It is eventually discovered the damaged Dalek suffered internal damage causing radiation leaks which led to Rusty's turn against his own. The Doctor repairs the damage but consequently causes Rusty to return to its normal state of hatred. In an attempt to turn Rusty "good" again, the Doctor merges his mind with Rusty to try and recreate the events that caused Rusty to turn "good". As a result, Rusty becomes good but also now holds an extreme desire to exterminate all Daleks. At the end of the episode, Rusty sends a signal for the Daleks to retreat from the Aristotle and goes on alone in a personal mission to destroy all Daleks.

Upgrades
Rusty originally appeared in Series 8, Episode 2 "Into The Dalek" as heavily damaged and rusted. Random wiring and fray is also strewn about the top of him. His second appearance, Rusty claims to have "upgraded" himself for "superior extermination" against the Daleks. Rusty's exterior is largely repaired, minus some dents, dings and carbon staining from plasma impacts.

His weapons have been upgraded, adding a quad rapid-fire turret system to his primary plasma "gunstick". Rusty displays the capabilities of his quad turrets in battling Dalek hordes, devastating dozens of them at a time during the incursion on the planet Gaia. He also has some sort of force-field which can be maintained for short periods of time before requiring a cool down period.