Irresponsible Captain Tylor. Captain Tylor drops into a coma due to a Mind Control chip implanted in his brain, so Yuriko and Azalyn have to enter his mind to fight it. The problem is this has only worked once in the past and the person entering the mind died, so they've no idea how to go about doing so.
Interesting variation on the trope: Instead of one character doing this to another, the audience takes a Journey to the Center of the Mind into the protagonist's head in the final episode(s) of Neon Genesis Evangelion.
Yu-Gi-Oh!: Shadi goes into Yugi's mind to investigate why he has a Millennium Item. He's understandably surprised to find not one but two minds there!
Yu-Gi-Oh! GX: During Jim's duel with Judai while he's possessed by Haou, Jim uses his magic replacement eye to take a trip into Judai's mind to figure out what's going on with him. He finds the former Ace surrounded by images of his dead friends and listening to to a repetitive loop of the reasons he sucks from that season's villains, sinking deeper into despair and farther out of reach.
In episode 12 of Pani Poni Dash!, alien technology causes Rebecca's class to get stuck in Himeko's dreamscape, where they encounter all matter of weirdness, including Idiot Hair on everything, a restaurant that serves nothing but crabs, and a fat thug who claims to be the Archangel Michael guarding the door to Himeko's heart.
The ending of Darker than Black turns into a Neon Genesis Evangelion-esque Journey to the Center of the Mind for Hei, after Amber uses the Meteor Fragment on him to trigger the Tokyo Explosion using his quantum-manipulation abilities.
With the help of a stray Unown, the Pokémon anime's heroes go into a Larvitar's mind to find out what exactly went wrong to make him so untrusting of humans... an incident involving poachers that left its Tyranitar mother injured and the two separated when it was still in its egg!
In the Fullmetal Alchemist movie, "Conqueror of Shamballa", the mindreader Noah takes the liberty of looking into Edward's past while he's asleep. In doing this she learns about his home and his brother.
Happens throughout Kaiba with the help of a small machine. People's minds are all libraries of various kinds, with their memories as books.
Happens frequently in Ergo Proxy, as this is the Proxies' preferred method of combat.
If Road from D.Gray-Man is not stabbing your eyes out for the hell of it, she enters your mind so that she can start raping it. Lavi did not enjoy the little tour of his own subconscious fears and insecurities.
In episode 75 of Sailor Moon, the titular Moon and the other senshi enter Chibiusa's mind to help her after she falls into a dark energy induced coma. In the anime, it also marks the first time we clearly see Sailor Pluto, the one who sends the Senshi there in the first place.
An interrogation technique in Naruto takes the form of this. The interrogators project themselves into their victim's head, often needing to fight through layers of protective genjutsu, until they reach the core mind. From there they can access and view memories.
The seal on the Kyuubi takes a form of this for Naruto. In the first part he needed to make a long trek through a maze of flooded corridors to communicate with the Kyuubi; by the second part the distance between their minds had been greatly reduced.
In Ciel The Last Autumn Story, one of the main characters falls into a coma after overusing her magic powers, and her closest friend and love interest have to pull one of these in order for them all to wake up safely.
Tatsuya from Hekikai No Aion went intro the protagonist's mind to wake her up from a Lotus-Eater Machine, to do that he must help her to realize that she's in a dream making her face the truth of Simon's death.
Nightmask of The New Universe had the ability to enter anyone's dreams, which he used to assist in psychotherapy.
In a villainous example, one story arc of the Sleepwalker comics had the Thought Police enter the mind of Sleepwalker's human host in an attempt to capture him.
The Don Rosa Scrooge McDuck story "The Dream of a Lifetime" has the Beagle Boys using an invention stolen from Gyro Gearloose to enter Scrooge's mind, where they end up reliving some of his many adventures. Donald Duck ends up going in after them, to try and wake them up before Scrooge wakes up with disastrous consequences for him and the Beagle Boys.
Done in Paul Jenkins' run on Incredible Hulk. Bruce Banner travels into his own mind to try and strike a deal with his Hulk personalities, each of which represents a different aspect of Bruce.
Grant Morrison's run on New X-Men featured a trippy, one-issue-long sequence with no dialogue (save one line on the last page), in which telepaths Jean Grey and Emma Frost travel into Cassandra Nova's mind in order to rescue Professor Xavier. In a later issue, when Jean discovers Emma's been having an affair with her husband, the confrontation takes place in Emma's mind.
In Wolverine Wolvie's body has been taken over by demons, prompting Emma to lead several members of the X-Men into his mind in an attempt to drive them out. In addition to people representing aspects of his personality and memories of comrades, Wolvie has doors in his mind dealing with specific subjects.
There was an issue of The Brave and the Bold (#31 of the revived series) that had The Atom literally shrinking down inside of the Joker's brain at the request of some scientists. He is given a tour through Joker's childhood after accidentally walking through the wrong synapses and absorbing some memories.
In a Justice League of America Fill-in issue by J.M. Dematteis, Martian Manhunter decides to show The Spectre that there is good in everyone by taking him, along with the rest of the League, into the mind of The Joker of all people, showing that in the impossible maelstrom of depravity and chaos that is his mind, somewhere, there is a small house with a kindly couple, representing the tiny bit of humanity the Joker still has.
The Calvin & Hobbes: The Series episode "Socratesland" involves the protagonists going to the center of Socrates' mind to repair a malfunctioning communicator chip, where the various aspects of his personality frolic about.
Queen Of All Oni: Uncle uses a spell powered by the Sheep talisman to send Tohru into Jade's mind in order to gather intel, only for Tohru to end up in Jade's Mental World and encounter the Aspects (Anthropomorphic Personifications of parts of Jade's mind) before being thrown out. This seems to have been for no other reason than to establish said Mental World and the Aspects as a recurring subplot.
The Doctor Who Fanfic After Life has the 9th Doctor going through this after his regeneration.
This is the entire premise of Being John Malkovich. Even Malkovich goes into his own mind, and the resulting surrealistic horror might qualify as terrifying if it weren't so goddamn funny.
This is the whole point of the movie The Cell, where in trying to connect to those who are in a comatose state, this normally therapeutic tool then gets used as a Mind Probe on a serial killer by the police and then turned around on the therapist by the serial killer into a Mind Screw. Later, the whole experience then makes the therapist improve on the whole thing to make it a true Journey to the Center of the Mind
Dreamscape revolves around government agents entering people's dreams for various purposes.
Harry Potter and the Order of the Phoenix: Snape introduces Harry to the magical ability of Legilimency, the ability to enter another's mind. We see Snape use it to peruse Harry's memories, we also learn that You-Know-Who used to use this skill to enter people's mind and implant visions so horrible they would be begging for death, and later we see a short, but trippy look inside Harry's mind as he and... well, You-Know-Who, battle for control of Harry's body.
All the occurrences happening to the hero in Gozu can be seen as this.
The Greg Bear novel Queen of Angels has a climactic trip into "the country of the mind" of a killer.
The Japanese novel Paprika (and the 2006 anime movie based on the novel) revolves around a device that lets the user enter another person's dreams, and what happens when said device falls into the wrong hands.
The sixth novel in the Young Wizards series, A Wizard Alone, has Nita and Kit travel into the mind of an autistic wizard.
This also happened during A Hat Full of Sky by Terry Pratchett. The Nac Mac Feegles entered Tiffany's mind in order to bring her some sheep's wool, Jolly Sailor Tobacco and turpentine, all things she relates with home and Granny Aching, to help her fight the Hiver that was controlling her mind.
There are also some short scenes in Thud!! which show Sam Vimes' mind as a permanently rainy, yet apparently empty city.
In Timewyrm: Revelation, one of the earliest Doctor Who New Adventures novels, Ace gets pulled into the Seventh Doctor's psyche by the titular Timewyrm.
In Simon Spurrier's Warhammer 40,000Night Lords novel Lord of the Night, the eldar trap Sahaal in his own mind. The psyker Mita is caught with him and at first thinks it's a daemon world. She explains the situation, he persuades her, and she frees him.
The protagonist of Norman Spinrad's story "Carcinoma Angels" goes on a journey into his own mind to attempt to cure his cancer. It works, but in a twist ending he can't find his way back out and spends the rest of his life in a coma.
In Andreas D. Hesse's Schatten über Fraterna (lit. "Shadows above Fraterna"), almost the whole story takes place in the protagonist's sister's mind, after his sister literally fell into a coma and he himself got hit by a truck. As every person his sister knows has an alter ego in her mind, equipped with power according to the relationship to her, he slips into the body of the duke of Fraterna, only to notice that the personification of his evil side has just stolen the most vital artifact in the whole world (the reason for his sister's coma). He is assigned by the queen (the representation of his sister) to retrieve said artifact.
The protagonists of James Morrow's Blameless in Abaddon enter the mind of God Himself, where they converse with Biblical characters and dinosaurs playing Scrabble. They discover that God is a Platonist, and hence everything they encounter is the Idea/Essence of that thing. They also learn some counter-arguments to the best theodiciesnote A theodicy is an explanation/defense for why evil exists if God is good; they intend to use them in the prosecution of an upcoming trial against... God Himself.
This trope is a typical day at work for a soulscaper in Burying the Shadow. They heal injuries and illnesses of the mind from the inside.
There's a light novel written by CLAMP named Yumegari (Dream Hunter), where the main character Tatsumi Honjou is a yumegari warrior who investigate the dreams of others and, if needed, dive into them. Every yumegari must be partnered with a yumemori who has to watch over the yumegari and their own dreams; Tatsumi's yumemori is a man named Kyousuke Kaga, and after her parents and predecesors die in the line of duty, Tatsumi goes to live with Kyousuke and his family...
In another, Picard and company attach Data's brain to the holodeck to enter his dreams so they can learn what he doesn't know that he knows.
In Deep Space Nine, O'Brien and Bashir interrogate a special agent this way. He turns the tables on them by creating a part of his mind that looks like the room they started from and trying to trap them there.
Red Dwarf: "Terrorform," the gang has to rescue Rimmer from his personal demons as manifested on a moon that has transformed itself into a manifestation of his psyche. In "Gunmen of the Apocalypse," the crew link a virtual reality machine up to Kryten's brain and enter his subconscious to help him fight off a computer virus that he had contracted in order to come up with an antidote.
Natch, there's a Buffy example. When Buffy goes catatonic in "Weight of the World," Willow uses magic to enter her mind.
Likewise in the Angel episode "Orpheus," the eponymous drug traps both Angelus and Faith inside his memories until his soul is restored.
In a Supernatural dream episode, Bobby was trying to get killed by his dead wife (who he killed), Dean fought and killed a doppelganger personifying his massive ball of self-loathing and Sam was tied down in a Christ-pose and used his psychic powers(?) to kill the Big Bad of the episode by bringing back his Abusive Dad.
In the 6th season's finale, Castiel breaks down Sam's wall and he has to find his way back to Dean and Bobby by finding and killing Robo!Sam and Hell!Sam, which the wall was making sure he never remembered.
And again in the 7th season mid-season finale, when Bobby is dying of brain trauma, and has to navigate his own mind to escape a reaper coming after him and to find a way out.
Invoked again in the 8th season, when Castiel takes Sam inside the mind of Fred Jones, a reality warping psychic, to talk him into regaining control over his powers since the latter buried himself too deep within his own subconscious to engage him in a more conventional manor.
In Heroes, Matt Parkman was forever going inside peoples' minds and dreams for various reasons. This came back to haunt him in Volume Five when he traps Sylar's consciousness inside his own mind, ultimately allowing him to take control of his body.
In the season four (two part) finale of House, Chase attempts to use medical hypnotism to unlock House's memories of a bus-crash. We can see both the inside of the bar he visited beforehand, and the bus he rode on. Most details are obscured or not present.
Played with in Taken. Several characters enter a crashed alien spacecraft, and see visions from their minds - a soldier sees his mother and her delicious cookies; one sees cockroaches, his greatest fear; one of the main characters sees her dead grandfather that she never met, who claims to be how she views him in her mind. In the end, it turns out the resident child psychic has been pulling these images out of peoples minds and making them see them - there wasn't even an alien crash.
One of the episodes of Disney Channel's So Weird had this as it's plot. Fi, Jack, and Clu end up going inside a young boy's dreams to find out why he's having nightmares. The nightmare-creature (represented by a huge mass of black mist) is constantly chasing them, and will only be defeated when the child stands up and faces his fears. What's he afraid of? His parents are constantly fighting and he's afraid that one of them will leave.
The episode "Numbskulls of the Beast" from The Legend Of Dick And Dom sees the heroes use magic to get inside the head of the Big Bad, to find where he has hidden the MacGuffin; They aren't particularly interested in why his wrath is represented as giant red teddy bears, or what's with his mind having security guards (who are flying Brooklyn-accented penguins) and cable cars.
In the Fringe episode "Lysergic Acid Diethylamide", Peter and Walter enter Olivia's mind in order to retrieve her conciousness after she is possessed by William Bell.
Occurs somewhat often on Kamen Rider Wizard, where there are Gates, humans with magical potential granted by an "inner demon" called a Phantom; if such a person crosses the Despair Event Horizon, their Phantom breaks free into the real world, killing them in the process. Wizard and Beast fight to keep existing Phantoms from creating more, usually by protecting Gates from falling into despair; if that fails, they can use magic to enter the Gate's mind and destroy their Phantom before it can manifest. The Underworld is usually depicted as a time-stopped version of the Gate's strongest memory, which becomes fragmented as they fall into despair and is repaired when the Phantom is destroyed. It doesn't happen very often, mainly due to the amount of expensive CGI it requires.
In an episode of STAR Street, the band take a trip inside Ashley's head after he starts behaving oddly. They pry through some of his memories and emotions before finding the cause of the problem, and even go as far as performing a song to get rid of it.
Ayreon's "The Human Equation": the protagonist, while comatose has a rather lengthy discussion with his emotions.
Similarly, "The Trial" from Pink Floyd's The Wall, which has Pink being confronted with his issues.
In one episode of And Sometimes Y, the hosts travel into the mind of a CBC Radio listener.
The Brain is a somewhat literal version of this, showing how the brain itself works.
In the Raven Loft adventure The Forgotten Terror, the deceased PCs' souls are trapped in a realm contained in the gemstone of an cursed dagger. In addition to areas that look like they are made of ruby, there are areas based various memories and aspects of the villain's personality. In the center of the realm is the villain himself, who is all-powerful within this realm. It's like a fantasy RPG version of the film The Cell.
In the French roleplaying game La Méthode du Docteur Chestel, the PCs are sent into the mind of a psychiatric patient in order to investigate his inner world and try to solve his mental problems. Gamemasters are encouraged to be creative with the (unfortunate) consequences of the therapy.
This is the fundamental premise of Dreamwalker.
The surrealistic indie rpg Lacuna Part I. The Creation of the Mystery and the Girl from Blue City
The players are agents of an unidentified organization dedicated to curing anti-social (i.e. criminal) behavior by entering a shared subconscious space with the criminal/patient.
They basically took the idea of the collective unconscious and turned it into a semi-tangible dream world where nothing is guaranteed to make sense, and it's populated with the unconscious, unwitting minds of everyone on the planet. Needless to say, there's a lot of strange symbolism to be had.
Tabletop Game/Champions Organization Book The Circle and M.E.T.E.. In the adventure "To Sleep, Perchance to Dream", the PCs must enter the mind of a comatose superhero and convince him that he's dreaming and needs to wake up.
The song "Amazing Journey" from Tommy: "Sickness can surely take the mind where minds can't usually go/Come on the amazing journey and learn all you should know..."
This is the central premise of Tim Schafer's Psychonauts— traveling into the minds of others and sorting out their emotional baggage (literally) and psychological problems.
Likewise, the action-adventure Alundra, in which we discover that people's dreams and subconscious minds contain a lot of block puzzles.
Dual Hearts and Alundra are created by the same development team. DH is practically a Spiritual Successor.
The "Dive To The Heart" segments from several Kingdom Hearts games. They generally take place early on and represent the player character's Keyblade powers awakening / resurfacing.
In Quest For Glory IV it's possible to see into the mind of a powerful enchantress in your dreams, by sleeping at certain places that have been touched by her magic. The dreams tell the hero what happened to her, foreshadow the climax of the game, and can vary slightly from character class to character class (characters who play as Paladins receive more information about what to do, while characters who have some magical ability have some dreams with a more romantic bent.)
In the Hitchhiker's game, Arthur Dent travels inside his own mind. He's looking for his common sense. It's pretty tiny, so it takes a while to find.
Breath of Fire uses this quite a bit. Every game in the series had a mental dungeon or two.
The surreal dreamworld side quest in Oblivion. It's the side quest where you help a comatose man wake up by retrieving parts of his sanity and reason to make him realize that it is All Just a Dream.
One of the scenarios in Osu! Tatakae! Ouendan 2 involves the Ouendan entering the dreams of a six-year-old boy to help him with his bed-wetting problem.
In the dating sim/RPG Ar tonelico, there exist machines called 'dive machines' that allow someone to travel to a Reyvateil's soulspace. The point is for the driver to deepen their relationship with the Reyvateil in order to generate new spells (and costumes). 'Diving' as a intensely intimate act and so a Reyvateil will only allow someone they like and/or trust to do so.
Final Fantasy VII: Tifa has to venture into the mind of her friend Cloud when he becomes mentally-quadriplegic and sits almost silently in a wheelchair, unable to do anything, after falling into the Lifestream. She, then Cid, become the main characters until Cloud comes round thanks to her help.
Sly 3: Honor Among Thieves sees Sly entering the mind of a trance-bound Panda King with a little help from the Guru. Once inside, he finds the Panda King locked in their Boss Battle from the first game, continuously reliving the moment of his ultimate failure.
In Shin Megami Tensei I, you have to enter the mind of the heroine to eradicate a demon that is devouring her from the inside.
One of the Quests in Romancing Sa Ga 3 had you go into a character's mind and save her from the being conjured by the poison she drank. Turns out that the entity causing her nightmares was also making her unable to walk; she becomes recruitable after said mission.
At least two examples in City of Villains. The villain Psymon Omega has you enter his mind and destroy his fear of commitment, the unknown, and the past. Similarly, the famous singer Johnny Sonata has you enter his 'personal hell' and destroy his soul so he can get out of a Deal with the Devil.
Neverwinter Nights 2: Mask of the Betrayer features sequences where you enter your own and other people's dreams (and fight inside them, and Your Mind Makes It Real if you die...), and the game ends with an extended where you enter your soul and have to prevent the Enemy Within from literally devouring your memories, and then banish him.
Gann can also wander around in your dream sequences, as can Kaelyn, Safiya, and Okku if you have enough influence with them at the end. Though only your romance option can enter the final sequence.
Used as a character upgrade in La Pucelle, which is the prequel to Disgaea. Complete with split personalities, Evil Is Sexy, laser swords and all wrapped up inside the mind of a rebellious princess.
Featured heavily in Disgaea 3, where it's called Mao's "heart" instead of his mind. Much of the plot revolves around Mao trying to defeat his psychological demons and "open his heart" by repeated trips inside his own psyche. In the end, it's the Power of Friendship and not these journeys that allows him to overcome his problems.
American Mc Gees Alice assumes the theory that Lewis Carroll's Wonderland was all a representation of Alice's subconscious mind, and in the game Alice retreats to Wonderland after her parents die in a fire, only to find Wonderland twisted beyond recognition by her own guilt and trauma, and takes it upon herself to defeat her inner demons and set Wonderland right once again.
In the Xenosaga series, there is a machine called the Encephalon which does this. In the entire trilogy, there have been three of these uses - once when retrieving KOS-MOS's memory banks from a black box in Episode I (shown as Miltia before and after the Gnosis incident began), and in Episode II, the crew has to dive into MOMO's head (shown as the subconscious of the girl MOMO was based off of, combined with a little of Jr.'s) to figure out what the hell Albedo did to her back during the Mind Rape of the previous game. The third incident is in Episode III, where the crew dives into Shion's subconscious (shown as Miltia before the whole thing with the Gnosis started) without even knowing they had done so. All three of them were pretty much Mind Screws, especially the KOS-MOS one (where it doesn't even use KOS-MOS's memories, instead an amalgamation of Shion and Jr.'s).
In Ar Tonelico I and II the main character can 'dive' into the 'cosmosphere' of the Reyvatails in your party, which is directly similar into exploring a person's inner mind and consciousness. It is a major game play mechanic as not only does it give you an intriguing look at their inner-selves, but is a requirement to unlock more powerful song magic for the Reyvatail you are diving into.
Silent Hill can be seen as this, with each game an examination of a particular character's psyche. Silent Hill 2 being the most obvious.
In Worldof Warcraft, the Old God Yogg-Saron will forcibly bring the players into his mind. There, they will bear witness of some acts that took place in the lore (or are currently taking place) in the form of illusions that they must shatter to access the brain, which must be damaged enough to remove Yogg-Saron's invulnerability. However, if they remain inside the Mind's Eye for too long, their Sanity Meter will instantly drop to zero, thus falling into the Old God's control
In the Wailing Caverns dungeon, the player is literally fighting creatures summoned by a sleeping druid. The final boss is essentially his mental jailer—when you kill it, he wakes up.
The Elder Scrolls V: Skyrim has a sidequest where you find Sheogorath taking a vacation in the mind of the deceased, criminally insane Emperor Pelagius III's mind, which he finds to be a nice vacation spot. To get Sheogorath to leave, and tend to his Daedric realm, you have to treat Pelagius' mental illness using Sheogorath's Daedric artifact.
Chapter 5 of Final Fantasy XIII-2 features this, unveiling the true feelings and wishes of both Serah and Noel.
In Arc Rise Fantasia, the party goes into Ryfia's consciousness in order to bring her back, after she's injured by an attack meant for L'Arc.
This is the premise of the game Earthworm Jim 3D; after being flattened by a cow, Jim ends up in a coma. In order to wake up, Jim (personifed by his ego) must navigate stages that represent different parts of his mind, ultimately doing battle with his femenine side; Earthworm Kim!
When the player presses the B Button during the important decision in The Halloween Hack, Varik enters Dr. Andonuts's mind and discovers the reasoning behind his insanity.
Dominic Deegan: Oracle for Hire loves this trope. Dominic adventures inside the minds of Szark Sturtz, kid brother Gregory Deegan, even his own, often fending off demons and necromancers with clear understanding and sheer strength of will.
9th Elsewhere is about the journey inside the mind of a troubled teenage author with writer's block, where the voyagers are the protagonist (the aftermentioned troubled writer) and the oddball muse assigned to her by a musing organization.
In Nodwick, the rest of the party enters Yeagar's mind to free him from the influence of a malign artifact. Yeagar's intellect is represented by an avatar of Artax (the party wizard), his conscience by Piffany (the cleric), and his insecurities by Nodwick (the henchman and the brains of the outfit).
Soul Symphony: Pretty much the story's premise. Main character Olivia is chosen to cure high school students of negative emotions by teleporting into their "Soul Worlds" and defeat monsters.
In The Tick episode "The Tick vs. Proto-Clown," The Tick gets literally knocked into orbit by the titular monster and goes on a journey through his own mind while the rest of the heroes have to deal with Proto-Clown.
In the Jimmy Neutron episode "I Dream of Jimmy," Jimmy travels into Carl's highly-illogical dream-scape to deal with his friend's recurring nightmare.
In an episode of Teen Titans, Cyborg and Beast Boy go into the depths of Raven's mind, where they meet embodiments of all the facets of her personality.
Duckman enters his own mind via hypnosis. Inside, he finds a monster made from his guilt that sabotages his ability to love women because he feels responsible for his wife's death.
Spongebob Squarepants did the dream version in the episode "Sleepy Time." Naturally, Spongebob managed to ruin the dreams of everyone in Bikini Bottom, and he awoke to find a group of annoyed friends and neighbors, insisting he stay out of their dreams because they get enough of him during the day.
The first episode of the Aardman Animations series Rex The Runt had the cast entering the mind of Cloud Cuckoolander Vince in a shrunken submarine in order to cure his Random Pavarotti Disease.
Instead, they re-tune him to BBC Radio 4.
The Batman had an episode where Batman and Dr. Hugo Strange entering the mind of the Joker to find out where he hid Detective Yin before she's killed by a bomb. The latter was quickly side-tracked by trying to psycho-analyze the Joker (which he was just looking for an excuse to do) while Batman pulled the Joker into his mind, and tricked him into revealing the location by making him thinking they already knew.
Danny Phantom has one episode where Danny's overshadowing ability extends to flying inside people's minds, specifically their dreams.
An opening of Arthur had the titular character enter the mind of his teacher and the mind of a classmate (later revealed to have dyslexia). The first mind was a giant homework factory, the second was a giant picture slideshow.
In the series finale of Mighty Orbots, when the title robots mistakenly believe they are slated to be scrapped, they decide to prove their worth by making a likely suicidal frontal assault on the series Big Bad, Umbra, a vast living computer in a Dyson Sphere called the Shadow Star. They physically penetrate Umbra's body, and find themselves literally inside his mind, doing battle with the physical manifestations of his thoughts. Against all odds, they win and destroy Umbra. They go home, and discover they were never going to be scrapped after all. They had misheard Rob planning a party for their first birthday. Sniff!
This once happened to Beetlejuice when Lydia became trapped in his mind. She ended up helping his pathetic, wimpy "will power" defeat "Prankenstein," the part of Beetlejuice's personality that goads him into playing tricks on people.
In the Venture Brothers episode "Assisted Suicide" the Monarch uses a mind-control machine to go inside Dr. Venture's brain to try and kill him from the inside out; Dr. Orpheus goes in after him to save Doc from the "possessing spirit." However, it turns out that Dr. Venture's mind isn't such a pleasant place to be, and a combination of traumatic memories and Freuidan archetypes send the Monarch running away screaming.
Doctor Henry Killinger does this to Doctor Venture as well in the episode "The Doctor is Sin."
In "Memory of a Memory" of Adventure Time, the main duo Finn and Jake have to retrieve a spell from their friend Marceline's memory so that she can awaken from her slumber. Turns out that they were tricked by Ash (Marceliene's Ex-Boyfriend) to retrive the memory of a break up so that they never broken up at all, Or to explain it another way the "Memory" that Ash was refering to after The Reveal was not the memory of the spell at all.
In the Halloween Episode of Invader Zim, Zim and Dib gets trapped in a world filled with twisted amalgamations of characters from the Crapsack World the show takes place in, evidently inside Dib's mind. Of course, when they try to escape into the real world, they find it too horrifying to bear and return back to their own (apparently less) hellish dimension.
The Duck Dodgers episode, "A Lame Duck Mind" has the Cadet, I.Q. High and the Villain of the Week going inside the tangled mess that is Dodger's brain. They're assisted by Dodger's Id, Super-Ego and Ego.
Candace, Phineas, Ferb and others go inside Candance's mind to retrieve a memory in the Phineas and Ferb episode "Monster from the Id".
In Young Justice Miss Martian breaks Kaldur's mind not knowing that he's a Reverse Mole. She is forced by Black Manta to heal him, so she and Artemis(disguised as Tigress) enter Kaldur's mind which is shown to be shattered by her attack.
In Batman The Brave And The Bold's Emperor Joker, when Joker gains Reality Warper powers Batman tricks him into entering his mind to drive him insane. The Joker is pulled into a world without Batman, meaning he has no reason to exist and is sane. In horror at this, the Joker gives up his powers to escape.