Self-Constructed Being

Having a corporeal form is pretty nifty, letting you do stuff like walk and talk. Sometimes, however you run into a problem: you have no body worth noting. Perhaps you're a robot or a Mechanical Abomination who's been reduced to a Heart Drive; a ghost who has to possess someone; or an alien who luckily can regenerate From a Single Cell. All of these are types of Self-Constructed Beings.

For a villain, this means another shot to Take Over the World; for a hero, this means a new chance to save it; and for anybody else, you get another chance to visit All The Tropes.

Characters who turn out to have this ability may Come Back Strong. If the Self-Constructed Being bringing themselves back to life is a human or other human-like being, they very well might be Naked on Revival. Better hope they can conjure up extra clothes to go with it!

Examples of Self-Constructed Being include:

Anime and Manga

Talpa of Ronin Warriors had to (re)build his body during the series.
Cell from Dragonball Z is the Trope Namer for From a Single Cell, so naturally this applies.
During the first two seasons of Monster Rancher, Moo is trying to dig his body out of the ice while the Heroes search for the Phoenix.
In Inuyasha, an early Monster of the Week was a mask that wanted a body. The bad news: it caused its wearer to decay rapidly - as in, from human to crude oil in seconds.
The Godhand from Berserk. Since they are not part of the physical plane and therefore have no physical bodies, they have to manifest through some material in order to make a presence in the physical world. But every 1000 years, they have the opportunity to reincarnate themselves into the physical world with a corporeal body.

Comic Books

In Watchmen, after Dr. Osterman (AKA Dr. Manhattan) is disintegrated by being trapped in an Intrinsic Field Subtractor twice, he spends some time slowly learning how to use his new powers to reconstruct a physical body to inhabit. It's not clear if he gains any benefit from having one, or if he just feels more comfortable being human-shaped.

Film

Hardware: A Wetware CPU skull has a bit more life than previously imagined.
Hellraiser: Frank Cotton built his body from a single drop of blood (and a few bystanders).
In Virus, an alien energy being uses machine and human parts to construct bodies for itself.
In the Watchmen film, Dr. Manhattan is seen rebuilding his body from elementary particles following his disintegration, as in the comics.

Literature

Journey to the West: The monkey king started as a rock.
The Myth Arc of the first four Harry Potter books covers Voldemort's various attempts to take a physical form, and ultimately rebuild his own body, culminating in his confrontation with Harry in Goblet of Fire. Subsequent books cover his ascent to power.
In the Star Trek Expanded Universe book of fan-submitted short stories, Strange New Worlds V, Commander Riker falls victim to a seed of Armus, which has been growing inside him for years and tries to pull a Grand Theft Me.
In the Percy Jackson and The Olympians series, the good guys are trying to stop Kronos from rebuilding his body (which was torn to pieces long ago) and returning to the world.
In Einsteins Bridge, The Hive have taken over several worlds by making tiny robots by light though tiny wormholes that builds into new Hive on that world.
In the in-universe dwarven myths of Discworld, their creator Tak wrote himself before he could write the world and the laws.

Live-Action TV

The Master in the new Doctor Who "The End of Time".
In The Sarah Connor Chronicles, the heroes discovered that Skynet was sending Terminators back in time to ensure Skynet's creation.
In Kamen Rider ZO, Doras was initially seen as a small sphere who absorbed various metal objects around him in order to take on his monster form.
- In Kamen Rider Double, the T-Rex Dopant is a head with legs until pulling in all manner of objects to form into a massive dinosaur.
Power Rangers SPD: The Man Behind the Man is a giant brain using the guys we thought are the main bad guys in order to build a Humongous Mecha body.
- Power Rangers Lightspeed Rescue: Though gaining a new body wasn't her main goal, Queen Bansheera was still sealed away and when brought into this world, her body was incomplete because the ceremony was interrupted. She spent much of the series as a face in a barely mobile chunk of rock until she absorbed one of her generals to complete her transformation. Just one of many Bad Boss moves that would lead to Diabolico's defection.

Tabletop RPG

In the Call of Cthulhu Dreamlands supplement, the adventure "Pickman's Student" has a proto-Great Old One named Ghadamon spend the adventure slowly taking over the body of a human being so he can enter the waking world.
In Exalted, The Fair Folk—eldritch maelstroms of passions from outside reality—must take an Assumption to enter Creation, lest they be Calcified. Such form tend to be dramatic to the extreme: an indescribably beautiful lady, a towering man-beast monstrosity, or an artist whose performances moves hearts (and steals souls).
In the d20 sourcebook Dragonmech, one of the character classes is a self-modified steampunk cyborg who eventually replaces all of their human parts save their head with metal robotic parts... with no mention of any sort of anesthetic.
- Dungeons & Dragons 3.5 edition's Eberron makes this an Artificer feat named "Self-forged". As in a Warforged that "forged" itself. The Artificer keeps their original race for a while, but eventually becomes almost entirely Magitek.

Video Games

Zelda II: The Adventure of Link has Ganon's forces plotting to resurrect him using you as a sacrifice.

Web Comics

In Schlock Mercenary, Petey is this to the evil Ob'enn. He went from a backup copy of the AI of a destroyed ship to being the nigh-omnipotent Fleetmind.
Xykon regrows his body as he rebuilds his army in The Order of the Stick and prepares to prove himself a Not-So-Harmless Villain.
Kid Radd: The Seer wanted to build a body in the real world so he could survive the destruction of the Internet and go on to destroy everything in the universe. He was defeated before this could happen.

Western Animation

In Swat Kats episode "Unlikely Alloys", a tiny repair robot balloons up to Humongous Mecha size after assimilating a lot of technology, followed by its creator.
Shendu's goal during Jackie Chan Adventures is the reconstruction of his body.
Vilgax spent most of the first season of Ben 10 in a tank regenerating.
Megatron spends the first season of Transformers Animated as a head attempting to build a new body.
Teenage Mutant Ninja Turtles:
- The 1987 cartoon has Krang, a small pink squid-like alien who is obsessed with getting his robot body working properly.
- In the 2011 series two part Season 5 episode "When Worlds Collide", K'Vathrak AKA the Newtralizer manages to reconstruct himself, as hinted at in The Stinger of his previous appearance ("Newtralized", where he was seemingly fried by a malfunctioning teleporter). He ends up developing electric powers and becomes The Dragon to Lord Dregg, proving to be an even greater menace to the Turtles during their battle and seemingly killing Michelangelo. Fortunately, Mikey reconstructs himself as well and takes the fight to the with powers of his own. He's destroyed when Salcommander smashes him off a cliff and into the core of Dregg's ship, which disintegrates him and his master for good.
X-Men: Evolution has this as a power of Apocalypse.