These are Tweet Cards from "Sonic Tweet". It is a twitter application made by Sonic Team as part of the 20th anniversary celebration. It was at: (http://sonic-tweet.jp/login/index.html). It is all in Japanese and was not intended for western audiences, however it is so cool, there is a ton of Brittish and American users on the app. What it is, is it has sprite animations of Sonic chasing Dr. Robotnik through Green Hill Zone. When the user types in a tweet, Sonic will spindash Robotnik and his life bar will go down. Sonic has a limited number of dashes but they regenerate after a half hour. Once Robotnik's life bar is finished his Egg-o-matic blows up and you are rewarded with a card. There are five hundred different cards to collect, each one sporting artwork from 35 different Sonic games. The more you beat Robotnik, the more experience you gain and you get to a higher level. With each new level, Robotnik will drive a different contraption from either Sonic 1, 2, 3, CD, & knuckles. It is highly addictive and cards are pretty cool.
This is a selection of 8 of the cards to give an idea of what they were like.
The application was closed at the end of 2011. (card submissions closed too, as their art is available elsewhere and they are virtual items) Info & card photos by SonicToast