Monsanto – Syngenta Mega Merger

I am working on an article about Monsanto – Syngenta Mega-Merger, which discusses the specific legal and practical bases to either support or opposed the merger.  I have a few questions that I need help with the details.

1.  What is the legal criteria that makes a merger a “mega-merger”?

I need to know what type of legal criteria makes up a merger and explain what a Mega Merger is.

2  What are the detriments of a mega-merger on the companies, consumers, competition, and the economy in general?