From Hasbro comes the following promotion: Spend $20 or more on Hasbro products and they’ll send you a free gift. Transformers is available as an option (looks like Power Core Combiners, Activators, Speed Stars, and Star Wars Crossovers are available). Here is the promotion’s page on Hasbro’s website, which links to a printable form with the terms and conditions.
Thanks to board member BWProwl for the information.