You can take your Crystal Critter to Kan the Geomancer in The Explorer's Camp. He will transform it into a live critter if you give him the Crystal Critter and 2000 coins. You also have the choice of making it a Chromatic Critter by giving him 3000 coins and a Green Crystal (it only costs 1000 coins, but he won't change it if you have only 1000 coins). When you feed them with their favourite emote then you get a few little pink crystals when you collect them you get 1 coin for each crystal. The critters size can be changed in your home via the home powers. You can make them really big or small.