Of the 16 characters, six are available from the start from a cast that includes Sonic, Tails, Shadow, Amy Rose and Eggman (from Sonic The Hedgehog), AiAi and MeeMee (from Super Monkey Ball), Ulala and Pudding (from Space Channel 5), Alex Kidd (err, Alex Kidd), Amigo (Samba De Amigo), NiGHTS and Reala (NiGHTS), Gum and Beat (from Jet Set Radio) and one more currently top secret character that we're forbidden to reveal for fear of severe reprisals and sullen rejection. And, no, it's not Ryu from Shenmue. Or the dragon from Panzer Dragoon. Don't be silly.
Here's the link -