A character who, while amazing in their own world, is either outclassed or unexceptional in this new one.
They're the iconic superhero in Everytown, America, but now they're in a world where everyone is a Flying Brick. A regional karate champion is knocked out in two hits in an international tournament full of masters. A Grade Skipper advances to a class where they are no longer the best student. They're a genius on Earth, but they get abducted and find that everyone off-world can compute advanced calculus too.
When Everyone Is a Super, no one is.
While Normal Fish in a Tiny Pond has a character go from From Zero to Hero due to the clashing circumstances of the new place they find themselves in, here it's the opposite. With Power Creep in place, a character's skill level is Overshadowed by Awesome when faced against peers and opponents who have normalized the thing that made our main character abnormal. When your hero is an Experienced Protagonist, a good way to create tension for them is to put them in situations where their experience would only help in the most basic ways.
Crossovers are very popular in this regard. Characters who are established as The Ace, the World's Strongest Man, the World's Most Beautiful Woman, or other archetypes defined by being winners in their continuities wind up encountering other characters who have faced foes with similar powers and abilities in their own setting and beaten them.
Sub-Trope of Fish out of Water.
Compare A Hero to His Hometown (local celebrities who're nobody outside their hometown), Always a Bigger Fish (where there is always someone better), Eviler than Thou (where someone "out-bads" the Big Bad), Fake Ultimate Hero (where the hero was never impressive to begin with), Graceful in Their Element (where the factors are environmental), Large Runt (where the comparison is size-based), Not Rare Over There (where a resource is rare in one place and common in another), Power Creep (where new content is always superior), So Last Season (where the way to defeat the last opponent won't work for the next one), Summon Bigger Fish (where you bring in a new threat to defeat the old one), Surrounded by Smart People (where The Smart Guy meets their intellectual peers), Villain Forgot to Level Grind (where the bad guy is easier to beat at a later stage), We Have Those, Too (where special qualities are rendered common), Well-Trained, but Inexperienced (a character is skilled, but lacks street-smarts), and Wrong Context Magic (where a character's abilities break the established rules of the new setting).
Contrast Instant Expert (when a character immediately becomes good at a new skill they acquire), Like a Duck Takes to Water (where a character thrives in their new environment), and Normal Fish in a Tiny Pond (an unexceptional character becomes exceptional in a new setting).
