You've got the 20 characters that are put into the game, Sonic, Mario, Silver, Bowser Jr etc. You can unlock each of their costumes in the Boutique. These can be put onto your Mii and can be bought for 300 stars each.
So by 5 gold/1st medals, you could unlock a costume with Shadow by getting 5 gold/1st:
Dream Snowboard Cross
Speed Skating 500m
And there would be a costume with Shadow, if you get it by now.
|Any of the 20 costumes||Win 5 gold/1st medals in any event/dream event.|