Realm Exclusive Effect

 66WESZQRaGo Dark World, here we come! The phenomenon where a character's powers, magic, appearance, and other attributes change when going from one world or another. A common example is an average person finds themself in another world where they may have superpowers or an item that can grant them one. After being sent back to the real world, the person would have no powers. However, the nature of the other world would have an empowering effect on people or certain items. Characters can use Phantom Zones in a world where their powers don't work, but this is temporary. This trope involves different worlds that characters can access through teleportation or portals. In the case of being Trapped in Another World, characters may become normal when they find a way back home; well, if they even want to go home. Other attributes can change involving this effect, such as appearance, tangibility, mentality, etc.

The purpose is to create contrast between the two worlds, making a more interesting dynamic for the audience. There are more things to think about when a character's powers can only work in one realm, developing the world.

Heavyworlder is a subtrope more common in Sci-Fi. See also HAD to Be Sharp for adaptations or training forced by harsh environment (natural or unnatural) on its inhabitants.

A staple trope of the Portal Fantasy sub-genre.

Anime and Manga

 * In Yumeria, anyone who enters Moera gains a colorful skin-tight outfit, including powers and weapons. Additionally, the main character can also give others a boost in power and combine their attacks.
 * Averted in Fairy Tail, where the characters are brought to Edolas and can't use magic unless they use specific equipment — or by swallowing a crystal.
 * In Dream Eater Merry, Yumeji has an ability he calls Lucid Gear to only be used in a Daydream.
 * There is also Ren Hinaki shares a symbiotic relationship with the Dream Demon, Quartier Latin. When in a Daydream, they can perform Dream Phase Union to fight other Dream Demons.
 * Played With in the manga Isekai Ojisan: when the titular character was dragged to a fantasy world. He initially didn't have any special powers there, but in the new world, he was given the gift of knowing the local language. This gift allowed him to learn their magic system. Then, when he is returned to the modern world 17 years later, he still has the knowledge and can use magic.
 * El-Hazard: The Magnificent World, one of the earlier Isekai licensed for release in North America, has four people gain powers when they are transported from Earth to El-Hazard. (Which powers they get depends on which continuity they are in.) At the end, at least one of the people returns to Earth.
 * There's no evidence that the main characters of Magic Knight Rayearth get to keep their newfound abilities when they return to Earth.
 * MÄR has people from Earth teleported to MÄR-Heaven who gain superhuman strength and better eyesight due to its lower gravity.
 * In The Devil is a Part-timer, magic on Earth is very limited compared to Ente Isla. Hence, demons and angels have to use other means.
 * Flip Flappers has Pure Illusion where those who can synchronize with a crystal called an Amorphous Piece can Flip Flap. This process gives the Flip Flappers superhuman abilities and weapons.
 * In Yuki Yuna is a Hero, girls who become Heroes through the Hero System go into another realm called the Jukai to defend the Shinju from the Vertex. They gain superhuman capabilities, armor, weapons, and a Fairy companion in this other reality.
 * Haruhi Suzumiya has Espers that cannot access their powers unless in a Closed Space or a similar dimension.
 * Corrector Yui and other Correctors use a ComCon to go into the ComNet. As a Corrector in the ComNet, they can use Element Suits that are given by Corrector AIs.
 * Fairy Tale Battle Royale has people who take the role of main characters in Fairy Tale settings. Depending on the character, they have the protagonists' powers if they had them in their story.
 * In Digimon Tamers, the Tamers and their Digimon partners can easily Biomerge in the Digital World to reach their Mega levels. In the real world, they cannot Biomerge due to Tamers not being made of data, so they have to do a workaround to invoke this ability.
 * Downplayed in Kinnikuman: By invoking Bergmann's Rule, Lunaight can tower over his opponent. This ability can best be used on Planet Earth, as that is where his ancestors originally came from. He can't use this ability in the Omega Cluster at all because that won't awaken his ancestors' genetics. Still, he's a powerful Chojin, so he doesn't need to rely upon Bergmann's Rule.
 * Downplayed in Kinnikuman: By invoking Bergmann's Rule, Lunaight can tower over his opponent. This ability can best be used on Planet Earth, as that is where his ancestors originally came from. He can't use this ability in the Omega Cluster at all because that won't awaken his ancestors' genetics. Still, he's a powerful Chojin, so he doesn't need to rely upon Bergmann's Rule.

Comic Books

 * People known as Travelers, Dreamland, face their phobia and gain a superpower based on it.
 * The original series Amethyst, Princess of Gemworld featured Amy Winston, an ordinary teenage girl who travels to the magic-ruled Gemworld and transforms into Princess Amethyst. While on Earth, she's a normal girl without any powers. On Gemworld, she possesses the magical powers of the House of Amethyst.

Film

 * Space Jam has any person who enters the Looney Tunes World gain attributes that make them more like cartoon characters, like being stretchy.

Literature

 * In The Chronicles of Narnia, the Pevensies are just normal British kids living in the 1940s on Earth, but in Narnia, they're powerful kings and queens with reputations similar to King Arthur.
 * On Mars (or "Barsoom"),John Carter of Mars gains superhuman strength and agility because of the planet's lower gravity.
 * The colonists of the world Pyrrus in Harry Harrison's 1960 SF novel Deathworld are Heavyworlders because Pyrrus has gravity twice that of Earth, but that's not where it stops. The entire planet is actively hostile to the human colonists — every single life form on it, down to the plants, is trying to kill them. The colonists are trained from the moment they're in diapers to kill or be killed, just to survive. The few that leave Pyrrus are unstoppable juggernauts off-world.
 * The Chronicles of Thomas Covenant: Covenant's wedding ring gives him enormous power while he's in The Land. On Earth, it's just a metal ring.
 * The Land's counts. It.

Live-Action TV

 * In Denkou Choujin Gridman, Naoto uses his Acceptor to fuse with the Hyper Police, Gridman, to fight Kaiju in the Computer World.
 *  Superhuman Samurai Syber-Squad's Sam can use his Samuraizer to transform into Servo and enter Syberspace whenever Mega-Viruses attack the cyber world.
 * In Zixx, certain people can access another dimension known as the Keep, a pocket dimension made by an ancient race. When any person enters this realm, they become something like a video game character with abilities and tools in this dimension.

Tabletop Games

 * An inverted example from d20 Modern's "Urban Arcana" setting: monsters from Dungeons & Dragons fall to Earth as "Shadowkind". Monsters, who are large physical combatants, aren't special on their home world. They, however, pose the greatest danger in the "real" world due to the high density of civilians, weapon restrictions, and the lower power level of heroes (especially heroic magic users). This is especially true of anything with damage reduction that requires magic to bypass it — in D&D one is expected to have a magic weapon by about level 4 and can find ways to have one temporarily from the first level. Still, in Urban Arcana any kind of magic weapon is exceptionally rare and likely archaic even if you find one.

Video Games

 * As seen in the video above, Deltarune's Dark Worlds can change Lightners' appearance with different clothes and give them magic and equipment. For Darkners, they turn into inanimate objects but can transform back when in another Dark World.
 * Tokyo Xanadu has the Eclipse, an overlap of reality with the Spirit World where certain people can use armaments called Soul Devices to fight against creatures called Greed.
 * Played straight in Persona 4 (as explained in canon with Persona 4 Arena), where the characters can summon their Personas while in the TV World. The characters within the setting believe that they can only summon their Persona in that alternate dimension. After encountering the cast of Persona 3 in the spin-off games, they discover that under heavy duress or using an Evoker they can summon their Personas in the real world too, albeit at a lower power level.
 * Persona 5's Metaverse can change the clothes of Persona users that have awakened to their potential. These outfits are related to their personality, much like their Personas. Model weapons can become actual weapons while in the Metaverse, too.
 * The Longest Journey has the two worlds of Stark and Arcadia; each society is based on science or magic, respectively. A shifter can go between the two and have access to magic while in Arcadia. Stark favors science and technology compared to the use of magic in Arcadia.
 * In Viewtiful Joe, the V-Watch cannot be used in the Real World, only in Movieland. The V-Camera, introduced in Double Trouble, is used to circumvent this limitation by filming Joe so he can turn into his alter ego.
 * The Mario Bros. in Mario & Luigi: Dream Team are as strong as they normally are in the rest of the Mario & Luigi series. But in the Dream World, Mario gains a mild boost to his stats, and his regular attacks are turned into crowd-clearing AoE moves.
 * The Holy Instruments, from Dual Hearts, can only take a tangible form in the Dream World that Rumble can wield.
 * In Tokyo Mirage Sessions ♯FE, there is the Idolasphere where monsters called Mirages live and feast on people's Performa (creative energy from people). Certain people called Mirage Masters bond with a Mirage by giving their Performa willingly to the monster, granting them powers and appearance similar to Mirages while in the Idolasphere.
 * In the Mega Man Star Force series, a compatible human and EM Wave Being can perform an EM Wave Change that allows access to the Wave World. The human can interact with devices, access the powers of the EM Wave Being, and can use Battle Cards as weapons.

Web Comics

 * In Layers, particular teenagers can teleport to another world called Layer and have various powers such as telekinesis.
 * In Her Summon, a summoner can temporarily transport Jin-Kyung to her world whenever she gets in danger. He gains magical powers by using mundane items as a conduit for spells but loses his magic when teleported back to Earth.
 * Hardcore Leveling Warrior has the virtual reality game, Lucid Adventure,
 * In the Dreamland Chronicles, Alex, when in Dreamland, has the Sword of Kings when he falls asleep. He also has magic armor and the ability to fly. Later on, his fraternal twin brother, Dan, gains the ability to dream and can lucid dream, giving him complete control over his dream form.

Western Animation

 * Midnight Patrol: Adventures in the Dream Zone has a group of children, and their dog is average. That is until they fall asleep to defend the Dream Zone from the Nightmare Prince with their powers.
 * Twelve Forever has three protagonists who can teleport themselves to Endless Island, where each has a unique power. Twelve get superhuman strength, Esther can create constructs from light, and Todd is a shapeshifter.
 * In Penn Zero: Part-Time Hero, Penn, Boone, and Sashi take over heroes in another dimension with superpowers or other abilities depending on the overshadowed hero. The villains, Rippen and Larry, much like the heroes may get powers, too.
 * In Code Lyoko, whenever a person gets Virtualized into Lyoko they gain a form and abilities that seem to be based on their personality.
 * From Chalk Zone, Magic Chalk is seemingly ordinary chalk, that while in the real world can open a portal to the zone, and draw anything in an artist's hands while in the titular world.
 * Played with in He-Man and the Masters of the Universe: in Orko's home dimension, he's an excellent mage and powerful enough to challenge the Istari, while on Eternia its magic environment crippled him so much that he comes across as inept. Even though he is weakened, he has been learning how to use magic from scratch in Eternia, which gained Adam's respect.
 * In The Owl House, Glyph magic is granted from a powerful substance known as Titan's Blood. In the Boiling Isles, Luz is able to cast this magic as it absorbs the magic around them. In season one, Luz and Lilith briefly fight in the human world, and Luz's glyphs do not work because there is no Titan's Blood. However, the first episode of season three, Thanks to Them, has Luz and her friends hunting for the substance, and thus the glyph magic works again near a bottle of it. Witches from the Boiling Isles, who have bile sacs which enable them to cast magic, are exempt from this effect, and can cast magic in the human world.
 * Dungeons and Dragons, the magical weapons given to the heroes by Dungeon Master only function in that realm. One episode where they actually make it back to their world, they find this out the hard way when Venger follows them, this condition not applying to his magic. They have to retreat back and goad him to follow, lest their world even survive for them to return to.