They are 20 different types of beans with faces, and they usually have a bit of unappetizing trivia to share with you. Mameshiba was created by Dentsu in Japan, as some form of self promotion (not sure exactly what, my guess is that they were trying to show how they could build a brand thru a mascot, and how it extends thru many other media, since they now sell them as toys, cell phone charms and so on).
The best of it all are the TV adverts. They are so random, that they are funny. YouTube “mameshiba” and you’ll see plenty of them. Very reminiscent of the MTV Watch and Learn sttuff.