New from the Supreme Court reaffirms veritable ironclad bar to admissibility of mediation communications in Simmons v Ghaderi today. Essential holding is that you can't prove anything at all using mediation communications and don't even think about it. That includes fraud, duress all other typical contract formation defenses. Here's a link to the opinion for you:

http://www.courtinfo.ca.gov/opinions/documents/S147848.PDF

"Here, the mediation confidentiality statutes made inadmissible all evidence
of an oral contract between plaintiffs and defendant during mediation."