I have to say that I'm a bit confused by the Elemental Market. I fail to see what filling it triggers in the mechanics of the game. Am I missing something obvious?
It just tracks how many points you get for your element rooms when you cap a tower, and at the end of the game.
Does that answer your question?
What happens if you do fill out a element? Is it worth -2? or 0?
It's worth -2