The mazoku in Slayers are beings of pure chaos that, as in the trope, feed on negative emotion, power black magic, and want to see the world returned to the Sea of Chaos. Fantasy RPGs like Dungeons & Dragons are an admitted influence on the setting, so it's possible they draw inspiration from that game's demons, etc.
In Bakugan, Mag Mel's armor is revealed to be this. Code Eve created it from the evil of former Big Bad Emperor Barodius and sealed him inside of it.
Umi Monogatari has Sedna, though not so much evil as sadness. She was born from the islanders' collective sorrow, which they cast into the sea rather than dealt with.
The Guardians of the Universe (masters of the Green LanternCorps) expelled all the evil from themselves in a similar manner to the race that created Armus in the Star Trek example below. Eventually, it took over the body of the guy who trained three different Golden Age heroes.
Mephisto once took an interest in Christ's Crown, New York, a horrible place with a dark and bloody history. Mephisto gathered power from the accumulated evil in Christ's Crown and used it to create his "son" Blackheart.
*The first rule of the Loc-Nar is never touch it while it is glowing.
Sephiroth in Final Fantasy VII: Advent Children. When he appears at the end of the movie, he is literally MADE of Jenova cells. He even bleeds it when cut. And when Cloud defeats him the excess Jenova cells making him up discorporate, leaving a beaten Kadaj behind.
Time Bandits by Terry Gilliam has Evil as the main antagonist. Once destroyed, a single piece/rock of him is overlooked in the cleanup, when Kevin's parents pick it up (after he warns them not to) they get vaporized.
In the 1980s Flash Gordon movie, the henchwoman General Kala's corpse visibly deflates and smokes as it turns into an oil spill.
Halloween's Dr. Loomis believes Michael Myers is this. It would explain his ability to come back from each increasingly over-the-top death.
"I met him, fifteen years ago. I was told there was nothing left. No reason, no conscience, no understanding; even the most rudimentary sense of life or death, good or evil, right or wrong ... I spent eight years trying to reach him, and then another seven trying to keep him locked up because I realized what was living behind that boy's eyes was purely and simply... evil."
The 'Mathmos' in the movie Barbarella is a seething psychedelic lake of slimy evil beneath the city Sogo.
The "mood slime" in Ghostbusters II is composed of negative human emotion. However, the fact that it feeds off emotion allows the Busters to convert several batches of the stuff into positive mood slime that is Made of Good.
The Evil Overlord Darkness from Ridley Scott's Legend is literally made of darkness, portrayed as the equivalent of evil. He's quite literaly the devil and wants to bring about an eternal night (even though it means the end of the world) because he needs it to thrive. Before his ultimate defeat he also taunts the hero that darkness can't exist without him.
Garmonbozia, in the David Lynch film Twin Peaks Fire Walk with Me is a substance in the Black Lodge described as being made of pure pain and suffering. Garmonbozia, in typical surreal Lynch fashion, manifests itself as creamed corn.
In earlier conceptions of the Orcs it was claimed they had hearts made from pure hate. And Thu, who eventually became Sauron, was made of pure hate.
The titular mini-black-hole in Angelmass balances the 'angel' particles it emits by becoming demonic itself.
The Big Bads in The Death Gate Cycle by Margaret Weis and Tracy Hickman were living avatars of evil who grew stronger in the presence of despair, rage and so forth. "I grow fat on your fear" isn't just a metaphor with them.
The Way of Kings: Although we don't have much information about them, the monsters that Dalinar confronts in one of his visions of the past bleed black smoke when wounded and dissolve once dead. They certainly sound like they're made of evil.
And in Words Of Radiance we encounter the stormspren, which are literally made out of hatred.
The Shadows in the Firebird Trilogy gain their name from their appearance (when not possessing a human): they are dark, nearly invisible, representing the fact that they are evil given form. Unlike many other forms of this, they are insubstantial and thus unkillable, although they can be kept at bay by prayer.
Dementors in the Harry Potter series are embodiments of negative emotion in general.
I am as much apart of this world as the light that warms the day.
Star Trek: The Next Generation: Armus, the eponymous skin in "Skin of Evil", is a being made up of an entire civilization's discarded negative thoughts and emotions. He killed Tasha Yar and was one of the few beings that the emotionless android Data felt should be destroyed without question.
Apparently just about every enemy the Power Rangers used to fight was this trope. When purified of evil at the end of the sixth season, most simply crumbled to dust.
Except Rita and Zed, who turned into a yuppie couple. And Divatox.
Subverted in Charmed. For the first four seasons, the Big Bad behind just about every evil being the Charmed Ones went up against was called The Source Of All Evil. Four years of Villain Decay later, however, and it turns out that "Source Of All Evil" is really just a title, and anyone in charge of the demonic underworld gets to call themselves that. The actual Source isn't the demon leader in question, but rather an amorphous force that gets inherited by whoever is currently in charge of the Underworld at the time, and gradually takes them over from the inside out.
Coulson: Do you need anything else before I go check on the device fueled by evil that's sitting in our cargo hold?
In Dungeons & Dragons 2nd and 3rd editions, demons and the like are made of evil, and angels are made of good. Devils are also made partially of law, while demons are made partially of chaos. Similarly, slaadi are made of pure Chaos and modrons of pure Order, a concept even more nebulous than being made of good or evil. Basically, any native of the Outer Planes is a physical embodiment of the ethical and moral principles they represent, given fleshy form. Anyways, this means fallen angels and risen demons still count as their original alignments for spell effects and Detect Evil.
In 3rd edition, any being with a subtype of 'evil' consisted in part of evil. Most of them were fiends (IE, outsiders with the evil subtype), which covers demons and the like, but there were exceptions.
Demons in Pathfinder are born from the sins of evil souls, in contrast to the Devils, which is what those evil souls become when they die.
The Warp in Warhammer 40,000 is made of all the emotions in the galaxy good and bad, but there's more bad than good. The Chaos gods have "good" traits that have been warped and amplified so much that to human sensibilities they become evil. For instance, Nurgle is a Friend to All Living Things— heavy emphasis on the ALL; Papa Nurgle loves his cute little parasites and pathogens, yes he does!
The Persona 2 version of Nyarlathotep is an Eldritch Abomination literally born of Humanity's collective evil, absorbing every evil ("evil" defined as "with the intent of causing any form of harm to anyone, even yourself") act, thought and desire. As Long as There Is Evil, he is an undefeatable mass of concentrated madness, woe, and discord, eternally hungering for more power.
In the second game, there is also a toxic liquid named Kegare - the ancient Japanese word for "sin" or "filth", extracted by the New World Order from their followers in their seminars. Supposedly the process "purifies" the attendees. It is literally concentrated evil.
In Mother, Giygas was an alien with psychic powers and a particularly sharp hatred of humanity. By the time Earthbound rolls around though, his hatred and power has grown to such a degree that it literally destroys his physical body and turns him into a floating, indistinct entity of pure evil.
Final Fantasy IV gives us another example: "I am Zeromus... I... AM... THE HATRED!"
In Ōkami, every villain disperses into a dark, malevolent cloud (with glowing evil eyes) once beaten, and flows back to the Final Boss. Which is pretty fitting, considering Yami is the source of all Evil/Darkness in the setting. Interestingly, one sub-boss, Red Helm, has it in his backstory as having spontaneously sprung from the spilled blood of Orochi, a bigger bad.
As is repeatedly stated in Kingdom Hearts, the Heartless are really just walking bags of malevolence without any true minds of their own.
Vanitas fits this even better than the Heartless. He's literally made from darkness.
Sephiroth appears to be made of evil as well. Specifically, Cloud's evil.
Dark Chips and Nebula Gray from Mega Man Battle Network are made entirely of negative emotions somehow encoded as data.
The monsters of Silent Hill are literally physical manifestations of different aspects of negative emotions (or events) created by the town itself, or Alessa, while she was still around.
Noob Saibot from Mortal Kombat is the leftovers of when the first Sub-Zero (from the original game and Mythologies) died and had his soul hurled into the Netherrealm, turning him into a wraith. His whole existence is entirely defined by hatred and scheming, as anything honorable that the original Sub-Zero might have had (which wasn't much to begin with) was purged.
M. Bison from Street Fighter himself isn't really Made of Evil but the power he uses (Psycho Power) is described as being pure negativity as energy. Negative thoughts, emotions, and general hatred manifests itself as this force.
The protagonist of Prototype is composed entirely of biomass infused with the Blacklight virus. It's the main reason he can take so much punishment: he has no bones to break or organs to rupture. Taken even further when it's revealed that he is the Blacklight virus.
Whenever "Sephiroth" from Final Fantasy VII shows up in the game before the Final Battle, it's actually a clone made of JENOVA cells, which is as close to being Made Of Evil as one can get in the setting. The actual Sephiroth is also made entirely of JENOVA cells when he appears near the end, since his original mostly (he was infused with JENOVA cells as a fetus) human body was destroyed when he fell into the Lifestream in the backstory.
All of the Prime Evils and the Lesser Evils of Diablo. No exceptions! Hell, the Big Bad himself became the game's equivalent to Satan.
The Lords of Shadow in Castlevania: Lords of Shadow. While their bodies started out physically human, they are being animated by the evil their original selves left behind when they ascended to Heaven. Having pure evil in place of a true soul seems to have had a detrimental effect on their bodies as well — only one of them seems to be able to maintain a fully human-looking disguise and all three have monstrous true forms.
The dragons in Dragon Valor are the evil in the world, and if a human has enough evil in his heart, he will turn into a dragon.
In Both Dark Cloud games the Big Bads have this feature and were created by The hate of a particular person due to war and Discrimination.
The Nasuverse has an odd example with its incarnation of Angra Mainyu. He was originally a normal guy whose fellow villagers wanted evil to have a physical form they could pin blame on, so they sacrificed him and began treating him as a God of Evil. Thus he's Made of Evil without actually being evil. When someone summoned him as "Avenger" in the Third Holy Grail War, his death and subsequent reabsorption by the Grail caused it to begin granting the wish he embodied, resulting in its corrupted state during the events of Fate/stay night and Fate/Zero. Fate/hollow ataraxia actually features Avenger fighting his own physical manifestation.
The black mud which pours out of the Grail is a physical manifestation of Angra Mainyu's curses. Contact with the mud can kill humans and even destroy or corrupt Servants. Gilgamesh's body and Kirei's heart are both made of it.
In World of Warcraft: Mists of Pandaria, the Sha fit this to a T. They are manifestations of negative emotion found in various places around the continent of Pandaria.
The Ashbringer (an incredibly powerful holy sword) was created from a crystal that was originally so evil that merely touching it turned a paladin's hand into a withered husk.
The main antagonist of the Soulcalibur series is not a man but rather a spirit of the cursed weapon Soul Edge. After being taken into battle time and again, all the bloodshed imbued what was a normal sword with a wicked, sentient spirit that would corrupt anyone who touched it into becoming a soul-draining slave for the sword. The sword's spirit (which is currently bound to a suit of armor so it may exist in reality) is Made of Evil.
The counterpart to Inferno, Elysium, that resides in Soul Calibur isn't any better morally. It's simply the opposite extreme on the Order Versus Chaos scale.
Mega Man ZX has Model W. Made of the soul of Dr. Weil, it corrupts anyone who fuses with it.
Dark Brain of the Compati Hero Series, at least until it appears in Super Robot Wars Original Generation, where it states it's the sum of all negative emotions and energies in the multiverse. Even if its body is destroyed, its essence will linger on, so long as there's an ounce of negativity present anywhere.
In Sailor Nothing, the Monster of the Weeks are created by pulling out the evil inside a person's heart and physically manifesting it. It's noted that the nicer a person is, the less evil they let out, and the nastier the demon created is. The demons are also highly influenced by the original's personality. This mechanic is explored thoroughly. When it gets turned on the series' titular heroine, however... Well, it's not good.
As depicted in 2001, The Makuta was this, or at least claimed to be:
I am that power. I am Destruction. And I will destroy you.
In the Sonic fanimation Nazo Unleashed, Nazo is stated to be the embodiment of the negative energy of the Chaos Emeralds.
The entity that possessed Nella's body in The Nostalgia Chick's "Dark Nella Saga" self-identified as a "quasi-demonic force of evil".
Black Mage from 8-Bit Theater fits this description. A conversation between him and the external physical manifestation of everything evil he has ever done went something like this:
Manifestation: Hey, here's a question. I feel a complete contempt for everything and the overriding need to burn the world. Is that normal? Black Mage: Are you filled with regret that, eventually, there won't be more world to burn? Manifestation: In the back, yeah. Black Mage: That sounds like my atrocities all right. Perfectly normal.
Aku himself is this as well. It even serves as his weakness: He's completely incapable of doing anything remotely good, to the point that it makes him predictable and even bites him in the behind a couple of times when doing good would have benefited him more yet he still couldn't help but be evil.
Darkwing Duck's evil side in "Negaduck" is both this and an Enemy Without, and presumably has both a sort of normal physical structure as well as being made of evil, because it's created when Darkwing is split into his "good and evil elemental particles" that they made up for that episode. Galvanized Negaduck in that episode is even more so, as becoming supercharged immediately turns him into a destructive Omnicidal Maniac and frankly admits how evil he is.
In Family Guy, Peter Griffin once purchased a Catholic toilet training book titled You're a Naughty Child, and That's Concentrated Evil Coming Out the Back of You.
In Teen Titans the demon Trigon the Terrible is referred to as the "incarnation of evil" and "source of all darkness."