For now, the set includes Sonic, Tails, and Knuckles. The best part about this period in Sonic's life is that there aren't really any more ridiculous characters to base toys on. No Big the Cat, no Cream and Cheese, and certainly no Shadow. Maybe Robotnik and a couple of mechanical Sonics later, but this collection is safe from the sidekick parade that has ruined the series.
The approximately 5-inch-tall toys will be released around the summer, for a currently unspecified price. Don't be surprised if they're expensive -- this is First4Figures, after all!