Coin ChallengesCoin Guy: "Oh dear, seems I have lost some of my prized coins. Can you please help me find them? I seem to have lost 8 Red Coins and 8 Blue Coins in each area. If you bring me all 8 Red or Blue Coins from an area, I'll have a special item or badge in store for you."
Basically, there are 8 Red and Blue coins hidden at each main area (Mushroom Plains, Koopa Islands, Flower Hills, etc.) and if you bring Coin Guy all 8 Red Coins and/or Blue coins from an area, he'll reward you with a rare item or badge.
I can't think of good rewards for this though.
