Which idiomatic phrase can be used to express 'showing all the hidden stuff' (it's supposed that nobody should find that out, some scandal things)?
Blow the lid off something.
"Spill the beans" or just "Spill it."
Uncover the skeletons in the closet or, similarly, show where the bodies are buried.
Do you want to describe an outsider discovering secrets or an insider revealing them? Most idioms that I can think of lean one way or the other.
"Shine a light on" and "Lift the veil" can fit.
The criminal fraternity might say 'peach', 'rat', 'grass' or 'cough'.
If you're letting someone in on the secret goings-on, you can be said to "open the kimono."
how about unhide all