Following up on the report on Rockman Gigamix 3, here's a nice (albeit small) look at two exclusive postcards slated to be given away to online customers. Individuals purchasing the book from Tanomi receive the card on the left, Fukkan shoppers the right:
As you can see, postcard artwork varies depending on the retailer you're buying the book from. What's more, Tanomi updated their listing with rules about a special sweepstakes. Apparently, if you collect five tickets found inside of Rockman Megamix volume 1 and volume 2 and mail them attached to the backside of the the Gigamix 3 postcard, you could be eligible to win an original cel drawn by none other than Hitoshi Ariga.
You can find all the details (in Japanese) at Tanomi's Gigamix 3 page. Hoping to get a more thorough translation soon!