Ghost Concept: ghosts don't smell like anything (similarly, they also can't smell anything) but they can evoke the memory of a scent to other people.
It's a reaction caused by their own emotional output, and the smell is determined by:
What emotion the ghost is feeling
The ghost's happiest memories tied to the emotion
For Example: when Danny is happy, he evokes the smell of wet grass (specifically when it's in the morning or late at night, when it's cooled down enough for precipitation to form), dirt, and laminated poster paper.
(because you can pry outdoorsy danny from my cold dead hands--)
Sometimes the scent can change depending on the environment or setting that causes the emotion. If Danny is in a winter/snow setting, the wet grass smell changes accordingly.
If he's sad and hurt, he smells like playground asphalt and woodchips, and sometimes, just faintly, of oxidized metal.
When Ember's happy, she evokes the scent of oxidized guitar strings, but also guitar polish and sheet paper.
And the stronger the emotion is, the stronger the memory is.
