In Adventure Time, Marceline's father, Hunson Abadeer, is sealed in the Nightosphere. Finn frees him, not knowing how evil he was. In the end, Finn manages to seal him back into the Nightosphere. Even worse is the Lich, the Ultimate Evil who was imprisoned inside amber within a great tree by the legendary hero Billy. He finally broke free during the season 2 finale.
Alfred J. Kwak: In one episode, Alfred encounters the Evil Spirit of Darkness, an ancient demon who caused so much torment and destruction that God locked him inside a magic bottle.
In Animaniacs, the Warner Brothers (and their sister Dot) were Sealed Zany in a Water Tower. In this case, it was more Sealed Chaos in a Can. The Warners keep breaking loose throughout the series and annoying people.
Beast Wars brought us Protoform X a.k.a. Rampage. He was the result of Maximal experiments to produce an immortal super-soldier by copying Starscream's mutant spark. They succeeded in producing an unkillable serial killer that slaughtered human and Cybertronian alike. After eventually capturing him, the Maximal Elders sealed in up in a stasis pod, then turned him over to Optimus Primal's crew to dump on some desolate asteroid since they couldn't figure out how to destroy him. Several adventures later and the monster was unleashed again and recruited by the Predacons.
Vilgax tends to be put in a can of whatever sort between appearances, be it a healing chamber, a block of ice, or a pocket dimension. He's slightly unusual in that we see him out of the can first.
Ghostfreak/Zs'Skayr is an odd example of evil that got sealed in a can accidentally, his DNA sampled for the show's Clingy MacGuffin so that the wearer can turn into him, and the personalities of his species being encoded in their genes somehow. Eventually, he gets loose and becomes Ben's Enemy Without.
Natron the First, who appears in the aptly named episode "Ancient Evil". After he's defeated and returned to his tomb, Mira melts the door to it. Hopefully this will keep him sealed.
Subverted with NOS-4-A-2, as he can still drain energy whilst in his coffin and his coffin can turn into a spaceship.
Camp Lakebottom: In "Pandora's Jock", the counselors banished the training titan Jacques the Jock to limbo by sealing him in an old television and tossing it into the shed. Naturally, McGee lets him out.
The Care Bears Movie had the Evil Spirit, whose can was a locked book of magic spells a young boy, Nicholas, opened. The spirit is powerful but, since it's confined to the book, needs Nicholas to cast its spells; he becomes progressively more evil in the process. The Power of Friendship helps him come to his senses and he helps close and relock the book, ending the threat.
ChalkZone had a two-part episode called "The Big Blow Up", which was about Rudy Tabootie opening the door to the temple of King Mumbo Jumbo and in doing so accidentally freeing a swarm of creatures known as Inflatermaus, who were imprisoned in there for centuries because their bite infects inhabitants of ChalkZone with a fatal disease called Balloonemia, which causes victims to inflate until they burst. Upon being freed, the Inflatermaus swarm begin to infect the people of ChalkZone again, leaving it up to Rudy, Penny, and Snap to find out how to cure Balloonemia and reimprison the swarm.
Code Lyoko: In the prequel episode, we discover that the dormant Supercomputer was sealing XANA for 10 years. It is Jérémie, by turning it back on, who unleashed the malevolent program (plus his future girlfriend) on the world.
The Courage the Cowardly Dog episode "Record Deal" had the ghost of a self-centered pianist named Velvet Vic, who was imprisoned in one of his records by Shirley the Medium. He's temporarily freed every time the record plays and attempts to make his freedom permanent by having Muriel take his place.
Nicolai Technus spent a fair amount of episodes imprisoned in Level Zero of the Doomed video game, until Danny freed him by deleting the game.
Fright Knight was sealed away inside a pumpkin, and was released first by Danny himself (accidentally), and later by Pariah Dark so that he could act as The Dragon.
Pariah Dark was sealed away to free the Ghost Zone from his tyranny.
Vlad seems particularly fond of releasing these - he released Pariah Dark unintentionally, and then later on intentionally releases Vortex on the world and then quickly loses control of him.
Any ghost trapped in the Fenton Thermos. Temporary, but still sealed away.
Technically not a can, but Pandora's box definitely qualifies.
The Ultimate Enemy: Dark Danny was sealed away in a Fenton Thermos and left with Clockwork, though for how long is unknown.
In Di-Gata Defenders the plot of the first season is for the titular Defenders to reseal an obscenely powerful entity known as the Megalith that the seasons' Big Bad used to take over most of the world a generation ago. However, the defenders decide on a change of tactics after finding out that not only has this thing been sealed and escaped numerous times in the past, but that it gets better at unsealing itself each time. The Megalith happens to be keeping another evil sealed in another dimension.
In the Five-Episode Pilot, Prime Evil spent a century imprisoned inside a cave thanks to Eddie, Jake, and their fathers the original Ghost Busters. After he tricks Belfry into releasing him, he starts using time travel to try and get even with the heroes as the series' Big Bad.
"Father Knows Beast" had Jake, Eddie, and their fathers fight a ghostly troll king named Slort, who was imprisoned in an urn by Jake and Eddie's fathers for 40 years until a boy unwittingly freed him.
The Flintstones: It can be argued the Great Gazoo was this to his people. He invented a death machine and they stuffed him in a satellite and sent him to Earth's stone age. Turns out in this case he's not such a bad guy, but it was a dangerous machine that got him sealed in his respective can.
The Freakazoid! episode "Invisibo" had an evil Egyptian prince with the power of invisibility who was buried alive in a sarcophagus sealed with a carving of a scarab, but ended up free to wreak havoc on the modern world when Dexter Douglas' older brother Duncan accidentally broke the scarab carving while trying to punch Dexter.
In The Godzilla Power Hour, the Cyclops was so invulnerable that even the Sufficiently Advanced aliens who discovered it couldn't destroy it, so they trapped it on an island behind an impenetrable force field. The sucker's so tough, even Godzilla doesn't successfully destroy it at the end, so the crew just ends up trapping it back behind its force field.
In Gravity Falls, the wax statues in "Headhunters" were locked away for ten years before Soos stumbled across them and they were able to seek their revenge.
"Aren't You Chupacabra to See Me?" had Billy buy an underworld videotape containing a chupacabra that would be freed from the video to feed on blood once the video was played.
"Pandora's Lunch Box" played with the legend of Pandora's box and had Pandora trick Mandy into opening her lunch box to unleash all the chaos and evil sealed within it. In the end, Mandy reseals the malevolent spirits back into the box along with Pandora.
"The Show That Dare Not Speak Its Name" had Billy scramble an enchanted puzzle cube, setting free a Captain Ersatz of Pinhead called Pinface.
Wrath of the Spider Queen has Arachnotaur, the Spider God of Anger, who was imprisoned in a carton of chocolate milk before Billy freed him by opening the carton.
Hot Wheels Battle Force 5: The Red Sentients were sealed away in five separate Battle Zones by Zemerick when he betrayed them. At the end of season 2, Krytus is freed by a traitor named Praxion (whom he promptly drops off a cliff) and proceeds to release the rest of his team from their own prisons. The rest of the Red Sentients were all frozen by Sage before they could join Krytus in his multiversal conquest. These are ultimately a subversion, as it turns out they're just as tired of the war as the Blue Sentients are when they're released and gladly make peace instead. They then reseal Krytus in a block of ice on a distant world as punishment.
Inhumanoids: All of the Inhumanoids were locked away for thousands of years before the beginning of the series. Tendril was chained up 2 miles underground, D'Compose was trapped in amber, Metlar held by a being with magnetic powers, and Sslither covered with concrete. And Blackthorne Shore freed all of them, the former three in the pilot alone.
There's also the Oni and Shadowkhan, who are all part of a Sealed Army in a Can. Their leader Tarakudo, an Oni Lord, was somehow reduced to a disembodied head and banished to another dimension, while his nine Oni Generals and their respective Shadowkhan armies were trapped in OniMasks that, should they all be reunited in one place, will be set free so they can start taking over the world. In the end, every single Oni and Shadowkhan are trapped inside a single mask that was placed on Tarakudo's face.
Some minor villains also got the eternal imprisonment treatment:
The Monkey King, an evil trickster who was turned into a puppet, but will be changed back into flesh-and-blood if another person pulls the puppet's leg (which turns them into a puppet in the Monkey King's place).
Hades, Greek God of the Underworld. Released by Felix Faust in the hopes that Hades will grant him "ultimate knowledge" in return. Hades naturally betrays Faust by causing him to instantly age to an old man since "Ultimately, pain and suffering are all humans will ever know."
Kim Possible had some sort of a sealed evil monkey man who petrified people in one episode. His name fit him perfectly, The Yono, and anyone who beats him gets to watch the one who released him petrified and re-sealed along with Yono.
Kong: The Animated Series: Chiros, the secondary antagonist. Imprisoned in a stone tablet that is implied, by Harpy cautioning the gargoyles moving it, would turn out bad for Chiros if it was broken (whether it will actually kill him or simply prevent him from being released ever again is unknown). It is also unknown why it was never destroyed the first time he was sealed inside it. At the end, Chiros is released, but Lua opens up a portal and Kong spins him by the tail and throws him back in, sealing him inside the tablet again. Kong immediately smashes the tablet.
The Legend of Korra: Vaatu, the Big Bad of Book 2 is an evil spirit who is the embodiment of chaos, is sealed in a dead tree in a desert by the first Avatar, in the Spirit World; Vaatu's design is similar to Aku's, as is his prison (evil spirit sealed in a dead tree in a swamp), which is itself a reference to Hexxus (toxic spirit sealed in a dead tree in a dead forest).
Looney Tunes: The singing, dancing frog who ruined a man's life in "One Froggy Evening" was placed into a cement slab and freed several hundred years in the future. The frog was also found by the man in question in that cement slab, so he may have been taken out of and put back into the slab many, many times by all the men whose lives he had ruined. This is based on the story of a real horned lizard that was sealed in the cornerstone of a courthouse (long before they were on any endangered species list). 31 years later the stone was opened and the horned lizard was alive and lived on for almost a year afterward.
Super Mouse in Pandora's Box was the rather awkward title of a Terrytoons cartoon re-enacting the Pandora tale with the mice/cats paradigm.
In ¡Mucha Lucha!: The Return of El Malefico, El Malefico was imprisoned in the core of the Earth for 100,000 years. He used The Flea to trick Rikochet into freeing him by reading a passage from the Code of Masked Wrestling backwards. At the end, El Malefico is defeated and he is sealed back up again.
My Little Pony: Friendship Is Magic: This is a fairly common way for villains to be neutralized, and a number of episodes feature a villain who broke out of one such can and needs to either be turned to the side of good or stuffed back in.
Nightmare Moon was sealed in the moon as "the Mare in the Moon", and remained there for a thousand years until her escape in the show's pilot.
Tartarus, a prison cavern guarded by the three-headed dog Cerberus, serves as a dedicated can for putting evil into. Its inmates have included the major villain Lord Tirek, who breaks free at an unspecified point and is sent back at the end of Twilight's Kingdom", a large variety of lesser but still dangerous monsters and Cozy Glow, who is sentenced to Tartarus after her defeat in "School Raze".
King Sombra was turned into a Living Shadow and imprisoned in the northern ice by Celestia and Luna. They were at least more thorough than with Discord. In the comics, King Sombra's backstory is revealed to be that he was created by the Umbrum, a race of shadow monsters that were sealed away underneath the Crystal Empire, to help them escape, but he was defeated and sealed away himself before he could release them.
In "Inspiration Manifestation", the tome was hidden away and locked behind a caged door for a reason. But Spike fails to notice any of this.
The Serpentine were split into their five respective tribes and locked underground in stone tombs following their defeat in the First Serpentine War. Lloyd would later release the first three tribes in an attempt to prove his evilness decades later. Pythor then finishes the job and unites the five tribes in order to conquer and destroy Ninjago.
A large portion of the Stone Army, originally created by the Overlord, were imprisoned underground and left dormant for thousands of years. They were uncovered during the Serpentine's burrowing attempt to bury Ninjago City, and were reanimated when the Great Devourer's venom dripped onto their bodies.
The Overlord becomes this in season 3 when his essence is sealed in a hard drive.
The Preeminent is an Eldritch Abomination that serves as the ruler and embodiment of the Cursed Realm. Trapped in an alternate dimension, she sends her ghost warriors, namely Morro, to find the Realm Crystal to free her in her quest to curse all Sixteen Realms (including Ninjago).
The Real Ghostbusters featured several episodes where the Ghostbusters had to deal with a supernatural being who was recently freed from their prison.
"The Boogieman Cometh" had the Ghostbusters seal the Boogieman within his own realm using an experimental Ghost Bomb. The Boogieman eventually managed to break free in "The Boogieman is Back" by feeding on Egon's fear when he was shaken from nearly falling to his death while on duty.
"When Halloween Was Forever" had Samhain, a pumpkin-headed ghost personifying Halloween who was freed from his enchanted prison by a pair of goblins. The same goblins freed him from the Containment Unit in "Halloween II 1/2".
In "Janine's Genie", Janine obtains a magic lamp that ends up freeing ghosts from another dimension. One of the ghosts tricks Janine by pretending to be a genie so he can keep her busy while he worked to free the other imprisoned ghosts.
"Knock, Knock" had some construction workers fail to heed an ancient door warning them "Do not open until Doomsday", resulting in New York being flooded with legions of demons and spirits.
The titular creature in "The Thing in Mrs. Faversham's Attic" was summoned by Mrs. Faversham's father decades ago and was bound to the attic until Mrs. Faversham hired the Ghostbusters to take him out after being bothered by the disturbing noises coming from there.
The Ghostbusters fight the Four Horsemen of the Apocalypse in "Apocalypse - - What, Now?", who were sealed within a book called the Codex of Saint Theopilus until Peter accidentally bought the book at an auction and Janine opened the book after bringing it with her on her lunch break by mistake.
Sir Breuse sans Pitie from "Hard Knight's Day", who was imprisoned in a tapestry by Merlin.
In "Cold Cash and Hot Water", Peter Venkman's father and Dr. Bassingame accidentally unleash Hob Anagarak, an ancient demon who was imprisoned in magic black ice prior to the Ice Age.
"Moaning Stones" had the Ghostbusters fight a demon known as The Undying One, who was sealed away until the three Moaning Stones of Tangalla used to imprison him were united and struck.
"It's a Jungle Out There" featured a demon with power over animals named Rall, who was imprisoned in a statue of himself.
Ray Stantz inherits a joke shop from his uncle Gaylord in "The Joke's On Ray". One of the items at the joke shop happens to be a chest containing a pair of imps who love causing mischief.
"If I Were a Witch Man" has the Ghostbusters summoned by the small town Lewiston to defeat Kestrel, a ghostly witch who was sealed inside a crystal ball 300 years ago by an ancestor of Egon's.
The antagonist of "Busters in Toyland" was Lothgar, a greedy demon who was sealed away in an enchanted clock and tries to trick Louis Tully's spoiled nephew Lawrence into taking his place.
The two-part premiere "Darkness at Noon" had the new team assembled to fight Achira, an ancient ghost who was kept in an enchanted prison underground. After she is trapped and put in the Containment unit at the end of the episode, it is shown that there were quite a few other supernatural entities that were kept in there.
"The Infernal Machine" has the team fight Luko, a ghost possessing technology who was trapped inside an inventor's creation for centuries until he broke free by possessing a child's toy robot.
Cohila from "The Crawler", a bug demon who was sealed in a sarcophagus and was kept dormant by having a magic jewel in his mouth until a pair of greedy thieves stole the jewel.
"The Luck of the Irish" featured a leprechaun being freed from a circle of enchanted stones and seeking revenge on the descendants of the people who originally imprisoned him.
"Eyes of the Dragon" had a bone-stealing demon named Gu Mo, who was sealed within a golden dragon statue.
In the backstory, the main antagonistAku was sealed away within a tall black tree by Jack's father (the Emperor of Japan) after Aku's initial rampage through his kingdom. In the first episode, Aku is released once again when the tree gets zapped by energy from a solar eclipse, allowing him to destroy human civilization and Take Over the World.
The three Minions of Set, a team of demonic warriors created by the Egyptian godSet. These three monsters were Nigh-Invulnerable and thus invincible against any mortal warrior, so the Pharaoh summoned the sun god Ra to imprison the Minions in a tomb. Thousands of years later, Aku frees them, and then sends them to kill Jack. Though they do a number on Jack, so much so that he is forced to flee whenever they find him, in the end Jack summons Ra for a second time; and Ra, apparently savvy that this trope never works, decides to just destroy the Minions with ease. After the series ends and the future is reset, its assumed the Minions are back in the tomb and will remain there assuming no one is foolish enough to release them.
In The Scooby-Doo Show episode "A Frightened Hound Meets Demons Underground", legend had that flying demons were sealed underground. The gang doesn't find any evidence to support there ever be real demons though.
The Scrappy-Doo and Yabba-Doo segment from The Scooby-Doo and Scrappy-Doo Show featured this trope in the episode "Vild Vest Vampire", where the titular vampire Count Zarko is released from his coffin after Scrappy and Yabba accidentally dug it up and is eventually tricked into going back into his coffin before our heroes proceed to mail the coffin to Transylvania. After first being freed, Zarko mentions his intent to terrorize Tumbleweed once more, implying that he was buried underground to put an end to his previous rampage.
In an episode of SheZow, BrouHaHa was imprisoned in a vacuumn cleaner, that also happened to be in a box, by Anges Monroe, the previous SheZow. He was imprisoned there for 61 years, until some unwitting customer brought it off Guy Hamdon, the current SheZow, in a garage sale.
The mischievous spirit in "The Box Of Dirty Tricks", which is sealed inside a box in an attempt to contain it from doing anyone any harm. Not that it stops the spirit entirely from doing its dirty tricks upon whoever possesses it.
Mystico the goblin from "Nobody Smurf", who was sealed inside a fountain and was accidentally released by Nobody and Clumsy Smurf when they knocked over a goblet near the fountain that they were not supposed to touch.
The druids in a tree in the episode "The Smurfs' Time Capsule". Only their leader managed to escape so that he could get the Moonrock Amulet and free his brothers when the light of the full moon hits the amulet. The Smurfs stopped his attempt and sealed the druid leader back inside the tree.
The evil wizard trapped in the Swapping Well. (Papa Smurf was the one who had trapped him there, it turned out.)
The Mad Artist Maestro, who was trapped in a painting for making art that could do that to living creatures, inadvertently released by Painter Smurf (who Maestro affectionately called his "apprentice" later; Painter later had to create the most convincing work of his life — as he said — in order to put him back.)
The Jackass Genie Genie Meanie from "The Magical Meanie" was forced to stay inside his bottle until he stopped being mean.
Sonic the Hedgehog (SatAM): In one episode, Robotnik steals a computer of magic spells from the formerly evil wizard Lazar, and Sonic attempts to get it back. When asked why he can't just destroy the computer, Lazar says that would release all the evil it contains.
In the Sonic Boom episode, "Closed Door Policy", Amy sells all of Sticks' possessions at a yard sale. This includes a surfboard blocking the entrance to the underground lair of the Froglodytes, a race of frog-like warriors. When the entrance is unblocked, the Froglodytes escape, capture Sticks, and attempt to sacrifice her to their idol god. Thus, it's up to Sonic and his friends to travel to the Froglodytes' underground lair to save Sticks.
SpongeBob SquarePants: In "Mermaid Man and Barnacle Boy III", the Mermaid Man and Barnacle Boy villain Man-Ray is shown to be imprisoned in frozen tartar sauce. SpongeBob and Patrick, who were watching over Mermaid Man and Barnacle Boy's headquarters in the superheroes' absence, end up accidentally thawing Man-Ray out. The villain escapes to resume wreaking havoc after tricking SpongeBob and Patrick into removing the tickle belt used to restrain him and exposing them to the Orb of Confusion, but he ends up doing a HeelFace Turn after finding that the tickle belt's made him unable to commit crimes without bursting into laughter.
The corrupted gems when they get bubbled. Centipeetle gets freed trice both by Steven but, before she gets retrapped the first time, she's a Sealed Good in a Can at this point and is permanently freed the second time.
Lapis Lazuli gets one when she gets trapped inside a mirror for a thousand years but it was more of a Sealed Good in a Can because they didn't know she was good, likely Steven let's her out.
Lapis Lazuli traps Jasper in a fusion in a Sealed Inside a Person-Shaped Can in the bottom of the ocean until the crystal gems freed her because she took over the fusion and become much more powerful resulting in a Never Punish Your Enemy in a Way That Will Grant Him More Power.
The Dark One from Super Robot Monkey Team Hyperforce Go!, who is so large he requires a planet for a functioning seal. Please see the first "Exaggerated" example on the trope's Playing With article for further details.
SWAT Kats: In the first episode, the Pastmaster is Sealed Evil in a Treasure Chest. We don't learn he exists until after he gets unsealed. There's also the Mad Kat the Insane Jester, who was sealed in a jack-in-the-box.
In the Tiny Toon Adventures episode, "The Looney Beginning", when Buster and Babs need to find villains for their series, they find a box known as the "Villains Box", that has signs with warnings such as DANGER!STAY OUT! and GO AWAY! written on it. Upon opening the box, it releases many of the series' villains, many of which are minor and one-shot characters, such as the Candy Bar Monster from the "Best O' Plucky Duck Day" episode segment, "Sticky Feathers Duck", The Devil from the ending to "Sawdust and Toonsil", The Metropolis Marvels from "The Acme Bowl", and Dr. Gene Splicer from "Hare Raising Night". Eventually, it gets down to Dizzy Devil, Elmyra Duff, and of course, Montana Max.
Total Drama: In Total Drama All-Stars, Mike's evil personality Mal was incarcerated in the same juvie Duncan was in sometime prior to the series. After he was pardoned from juvie Mike was able to take control and seal him in his mind, until years later Scott accidentally hit him as Manitoba Smith in the head with a shovel, partially freeing him.
For 4 million years, the Ark held the Decepticons and Autobots in stasis, under a volcano... until volcanic activity shook things up and woke up the evil Decepticons.
In Cosmic Rust, there's a dead planet with radio beacons warning travelers to stay away or die horribly. The Decepticons plunder it, and in the process, catch the metal-eating plague called Cosmic Rust.
In Return of Optimus Prime, the Hate Plague spores were sealed inside a star after their last outbreak. Unfortunately, the star went nova.
Starscream himself could be considered Sealed Evil in a Can in the episode Starscream's Ghost; his ghost first appears after Octane tumbles into the Decepticon crypt and knocks over the ruins of Starscream's grave marker.
Deconstructed in Transformers: Prime. After Unicron's defeat by Primus, his body was cast away into the depths of space. His gravitational pull attracted matter over billions of years which coalesced into the Earth itself. Unicron's physical form is the Earth's core, but he can control the mineral deposits on the surface and create golems of himself, among other things. Played straight when Optimus traps Unicron's Anti-Spark (his soul basically) inside an indestructible reliquary in the series Grand Finale.
Trollhunters: A major part of the series' Myth Arc is that Gunmar and his Gumm-Gumm army have been trapped in the dimension known as the Darklands for centuries, with his remaining minions on Earth trying to open a portal to free him. He successfully escapes midway through Season 2. Another example is revealed in Season 3, when we learn that Gunmar's master Morgana has been imprisoned inside the Hearthstone that Trollmarket is built around for just as long. She's freed near the end of the season, but in the Grand Finale is imprisoned again by being thrown into the Shadow Realm and having the only apparent means of opening portals there destroyed.
Simon and Snarf in Trollz; while the Magic of the Five was sufficient to release Snarf, Simon had to trick the girls into helping him, as he could only be freed by someone pure of heart helping him of their own free will.
The Venture Bros. - Dr. Orpheus, threatened in a diner by two "foulmouthed rednecks", magically traps them in a 'homeboy' figurine he'd earlier bought from a vending machine.
The Visionaries episode "Dawn of the Sun Imps" had the titular Sun Imps, who were six yellow beings who loved to cause havoc before they were sealed in a crypt that was subsequently buried. Cindarr is tricked into using his power of Destruction to bust the crypt open and set the Sun Imps free, resulting in the Sun Imps causing trouble for Spectral Knight and Darkling Lord alike before the two factions team up to reimprison the six nuisances.
Valtor from Winx Club may count as sealed evil in a block of ice, until the Trix released him in the beginning of season three.
The position of Phobos and several of his most powerful minions for most of the second season of W.I.T.C.H. until he gets released by the heroines. Nerissa was also once a Sealed Evil In A Can, but she escaped several decades before the series begins.
She ends up being Sealed Evil in a Jewel at the end of Season 2.
Wuya from Xiaolin Showdown was trapped in a puzzle box for 1,500 years until Jack Spicer freed her unwittingly.
Likewise, Hannibal Roy Bean was trapped in the Yin-Yang world for nearly as long until Omi freed him unwittingly.
And then there's Sibini, who was trapped in the Mosaic Scale until "The Evil Within".