Long, long ago, there existed a terrible evil. The people of the time managed to defeat the evil and seal it away never to return. There's just one problem: they may have sealed away the being itself, but they didn't manage to completely seal away its power.
To be clear, the evil in question has been sealed away, but in a way that allows it to still influence the mortal world, most often in destructive ways. In religious and mythological uses, the evil is usually not aware it has this ability. In fictional stories, especially in the Horror genre, it is likely to be aware of its ability to affect the mortal world, and will probably use that influence to facilitate its release.
Is a Subtrope of Sealed Evil in a Can. If the evil is sealed within a physical object, that object is likely to become an Artifact of Doom. Compare Might as Well Not Be in Prison at All, for when this applies to mundane criminals. See also Evil Is Not a Toy and Made of Evil.
[[folder:Anime and Manga]]
Soul Eater: The Demon GodAsura was sealed in a bag made of his own skin. Even after this, his madness is strong enough to warp the statue of a god holding his container and make everyone who tries to approach it see horrible hallucinations. However, it is only when Asura is freed that his madness is able to spread all over the world.
This is how Winnowill from ElfQuest ends up when Rayek traps Winnowill's soul inside his own. Winnowill is mostly contained but occasionally is able to either affect Rayek's actions or even lash out with her own magic powers.
Shadowpact reveals that the slumbering, highly powerful and very evil sorcerer Dr. Gotham has been sleeping beneath (wait for it) Gotham City for centuries. He inadvertently influenced the city into becoming a crime ridden cesspool with a penchant for attracting costumed lunatics.
In Time Bandits, Evil has been locked away in the Fortress of Ultimate Darkness by The Supreme Being. He plots on acquiring the McGuffin map that would allow him to escape and wreak havoc upon all creation. Albeit he's locked away, he can still Mind Control the weak-willed bandit across time and space to lead the group into his lair with the coveted map.
Prince of Darkness. The Anti-Christ is trapped inside a glass cylinder inside a church. It sprays a liquid at one of the people researching it and takes control of them, then has that person spit the liquid at other people to possess them as well. It also uses Mind Control on street people who live near the church to surround it and trap the researchers inside.
In prologue to the Space Wolf novel Ragnar's Claw, set about a century after the rest of the book, a Chaos cultist tells Ragnar that "Botchulaz sends his regards." In the book proper the Inquisition and Ragnar's squad of Space Wolves end up having to repair the seals on an eldar construct keeping a Great Unclean One confined.
Discworld: In the very first book, the prison of the Soul Devourer is untouched by time, and avoided by most wildlife because of that.
In The Wheel of Time, the Dark One is sealed outside of reality. In the Age of Legends, a bore was made into its prison, and it wreaked havoc across the world until a seal was made. Throughout the series, the seal is weakening, and the crux of the plot is finding a way to restore it before the Dark One can escape and unravel the world.
[[folder: Live Action TV]]
In Buffy the Vampire Slayer season 1, Big BadThe Master is trapped underground inside the Hellmouth but he has minions who work to free him, Darla being the one with the most character development. He almost gets out a couple of times, and during one episode where people's nightmares come true he's seen free and walking around Sunnydale in Buffy's nightmare.
The Master: I am free because you fear it. Because you fear it, the world is crumbling. Your nightmares are made flesh.
[[folder: Religion and Mythology]]
The titan Typhon from Greek Mythology. He was sealed away along with most of the other titans, but his roars were capable of causing volcanic eruptions across the world.
Loki from Norse Mythology was sealed away in an underground vault, with a snake drooling venom onto his face. His beloved wife is usually there with a bowl to catch the poison, but when she has to empty the bowl Loki's agonized thrashing causes earthquakes.
In the Forgotten Realms setting, after Cyric, god of murder and lies, murdered Mystra, goddess of magic, in 1385 DR and caused the Spellplague, several other gods worked together to imprison Cyric in his home plane. He can still grant spells to his worshipers but he can't affect the Prime Material directly and is slowly going (more?) insane. Strangely his co-conspirator Shar seems to gave gotten away scot free.
Module WG4 The Forgotten Temple of Tharizdun. Though the evil deity Tharizdun has been sealed away, his power can still affect creatures that enter the title temple if they touch certain places or objects.
Module OA6 Ronin Challenge, Episode 6 "Keluh Valley". The powerful being known as the Earth Spider is trapped in the Realm of Mirrors, but it can still communicate with its worshippers in the Keluh Valley. It orders them to look for a woman of the Wood Spirit people so it can marry her and be freed from its prison.
Module B3 "Palace of the Silver Princess". Arik (AKA Arik of the Hundred Eyes) is an ancient, evil being of great power. He was banished to a special dimension centuries ago to be imprisoned for all eternity. However, he has managed to send one of his eyes into the campaign world, where it works to open the dimensional barriers and free him from his imprisonment.
Call of Cthulhu. In his tomb on the sunken isle of R'lyeh dead Cthulhu lies dreaming. True to the source material Cthulhu is capable of communicating with his followers through their dreams. In the Cthulhu Now supplement adventure "Dreams Dark and Deadly", Cthulhu was able to contact the minds of dreaming people and tried to use their magic points to create an avatar of himself that didn't need the stars to be right to exist.
A specialty of daemonically-possessed weapons in Warhammer 40K / Warhammer. Using them gradually brings you under the daemon's control (or just makes you go insane, which is often the same thing). Dawn of War II: Chaos Rising has an entire game mechanic based on this, to determine which member of your squad becomes the traitor.
Organization Book 3 The Blood and Dr. McQuark. Inhuman creatures who are virtually immortal, immensely powerful and hideously evil are trapped inside the Earth. They can contact humans and corrupt them to gain followers, but can't escape on their own.
Adventure 4 The Great Super Villain Contest. The Crimson Claw's secret masters once ruled the Earth, but the power that banished them set up barriers to keep them out. The only way they can return is to be summoned by a creature on this side. They have sent the Crimson Claw to provide three devices - the Emerald Eyes of Azog - to the most powerful supervillains. In addition to being able to see through the Eyes, the secret masters can cause them to act as gates to allow powerful demons to enter our reality.
Ganon was sealed away into the Dark World by the seven mages in The Legend of Zelda: A Link to the Past, but used his evil influence to recruit Agahnim. The mage infiltrates Hyrule Castle and sets into motion Ganon's plans to capture the seven maidens and break the seal made by the seven sages.
In the Mass Effect franchise, the central antagonists, The Reapers, sealed themselves away 50,000 years ago to wait for the right time to return. However, they left one of their own behind to observe and report. Even after that one is killed by the central protagonist, however, The Reapers still have thousands (if not millions) of Slave Mooks that they control, as well as the ability to make more almost any time they want. They can even Assume Direct Control of these mooks to directly speak to, and deal with, tougher threats.
In Eternal Darkness, Mantarok the "Corpse God" is in its death throes for more than seven centuries. However, it had already set a chain of events in motion by this time that manipulate several pawns and allow them to defeat the other Eldritch Abominations that bound him.
The other Ancients qualify as well. They're sealed in the great Darkness with only Mantarok to keep them in check. The events of the game involve one of them (actually all of them) using their various pawns, artifacts, and minions to simultaneously get themselves free as well as completely screw over the others.
City of Heroes. The demon Bat'Zul, which was sealed under Cap Au Diable in the Rogue Isles. He was sealed properly, until a Mad Scientist realize he could drain electrical energy from the demon to provide cheap and efficient power to the city... with the small side effect of lightning demons occasionally jumping out of the power lines.
In The Secret World, most of the cans are a bit leaky to begin with, with The Filth, a tarry ooze that causes nasty tentacled growths and even nastier insanity, being the most obvious sign. Some of the sealed evils can influence the world in other ways, too (Aten was able to keep its cult going despite being imprisoned, for example).
Epic Mickey: The Phantom Blot is a being of paint and thinner who spilled over Wasteland and spread destruction all over it. They managed to seal it back into its jar, but little blotling enemies keep leaking out of it.
In Dantes InfernoSatan was able to send his essence out from Hell and corrupt others to do as he wishes. He escapes his secondary prison (a giant Eldritch Abomination body) to fight Dante, but in the end, Dante uses the souls he absolved in Hell to defeat Lucifer and seal him back in the 9th Pit of Hell (with a stronger seal this time). However, he somehow manages to escape as the ending reveals he transforms into a snake.
Corypheus, the ancient sentient Darkspawn in the Dragon Age series, has been sealed away by the Grey Wardens since the First Blight, but is still able to telepathically enthrall individuals in the general vicinity of his prison, who then devote their lives to finding a way to break him out (which involves trying to kill the Player Character and his/her sibling in the Dragon Age II DLC Legacy).
In Final Fantasy V, Exdeath spends the first half of the game sealed away by the crystals, but he is still able to command monsters and to mind control some people in order to bring about his release.
[[folder: Web Comics]]
In MeatShield the ancient half-dragon demon Disparoxus is imprisoned in a magic seal inside a cave, but if somebody actually comes into the cave and finds the seal he can talk to them, and he gives one guy a medallion the lets him talk and cast spells through it (although he only uses the latter when his dupe outlives his usefulness).
The Snarl from The Order of the Stick was sealed by the gods in a jail that used the entire planet for the lock. However, five rifts have formed in said jail, one of which allowed it to reach through and kill Soon the paladin's wife. Soon's party locked the rifts with impassable gates, but now four of the five gates have been destroyed, and the rifts they covered have grown huge.
anti-HEROES has the demigod Arderas, who was imprisoned in a special demiplane by a fiend who used to be his colleague. However, he managed to kill said fiend halfway through, leaving enough gaps in the prison for him to talk to mortals. At the time of the story, that ability had earned him his own city and army.
[[folder: Western Animation]]
Mighty Max: Skullmaster spends the first season sealed up inside the Earth's core, but still manages to control his various minions on the surface.
In Danny Phantom, Sidney Poindexter's spirit is trapped in an alternate spirit dimension version of 1954 Casper High. The mirror he left behind in his old locker, 724, serves as a portal between the worlds. Poindexter can't normally cross through the mirror portal, but as he witnesses several bullying attempts on the present-day real world side, he is able to use his ghostly power to reverse the bullying and turn it back onto the bullies.
Five hats means that five tropers think it is ready to publish.
You are saying that you think this draft is ready to be published. That means the description is not ambiguous,
it doesn't duplicate an existing trope, there are at least three examples, and the title makes sense.
Is that what you meant to do?
You are saying this draft has a ready-to-publish hat it does not deserve and you are taking it back.