In this article on Cracked.com, I discovered this gem of a phrase:
...Batman is the personality-shelf where Bruce Wayne stores the crazy-plates...
...and I thought it was a fantastic phrase. Then I looked at it some more, and I wondered if it was just a simple metaphor, or whether there was a name for this kind of imagery.
My thinking is that to be a metaphor, it could have simply been:
...Batman is the shelf where Bruce Wayne stores his crazy...
The Batman persona is a shelf, and the crazy is a thing that goes on the shelf. That's a metaphor.
The line in the article, however, invents two new things that clearly refer to existing ideas, but aren't the same as them.
So they've invented the concept of "personality-shelf", and said that's what Batman is. The same with "crazy-plates": even though it seems like pure whimsy, it provides some symmetry, clarifying the image and serving as the punch-line.
I looked up "inventaphor", but that's not a word that Google knows, so I assume that's not what this is called.