Is there already a trope for this? I looked, but I can't really figure out how it should be called.
The characters return victoriously from the otherworld! Sadly, for the spectators, very little has happened in that time, and the heroes have to grudgingly admit they can't prove that they just saved the world.
But hey! What's that? The sidekick has unwittingly picked up and put in his pocket a sparkly thing that came with them from the otherworld! Proof!
Sometimes, the characters might show this proof to others, sometimes they might just smile and know that while nobody else believed them, 'they' will always know what they saw was not just a dream (Character Building
- A Hat Full of Sky: When Tiffany returns from Death's Domain, her boots are full of black sand, even though she never left the place she was standing in her world.
- [[Contact]]: Jodie Foster's character only fell through the machine in our world, and the film came out as only noise. However, there was recorded film for the entire time she spent in the alien world.
There are also a lot of kids' series where the characters bring a cute sidekick monster from the otherworld, but I'm not sure those should count for this trope.