How to get things
Shells come from visiting (25 a day), unlocking achievements in any game (6 each) and finishing sets. You start with 150. Shells are never sold.
Coins come from achievements in released games (see the Coin Shop). A few classic pieces cost coins.
Island Pass tiers, set rewards and seasonal events give the rest. Event pieces are free to claim while the event is on and come back every year. Every price is shown up front. Nothing is random and nothing costs real money.
