Got an email with a printable coupon/barcode that will give a cert worth $5-$5000. Here are the details.
Bring the Mystery Rewards certificate to your nearest Best Buy® store by 11/16/13. Ask a Customer Specialist to scan it to reveal the value. If the value of the Mystery Rewards certificate is: $5 to $500, you may redeem it immediately through 11/16/13 at participating Best Buy stores (not valid online) 250,000 My Best Buy points (that's $5000 in My Best Buy certificates), please call the toll-free number printed on your receipt by 11:59 PM (PT) on 11/22/13 Redeem your certificate in a single transaction with a total purchase price equal to or greater than the value of the certificate.
I do not know what triggers it. I am Elite Plus.