According to the announcement, Amy Rose DLC for Sonic Superstars will let you play as the character in her more modern attire for free. You only need to sign up for the Sonic Superstars newsletter ...

In addition to this, Sega is also offering a free LEGO Sonic Skin which you can also obtain via the Switch eShop. There doesn't appear to be a time limit on this one, but if you do want it, it's ...