Crystals are objects you need to collect in a stage. There are three types of Crystals: Red Crystals, Green Crystals, and Gold Crystals. Red crystals are crystals you must collect in order to complete a stage. They only appears in Marble Mania. Green Crystals only appear in Marble Mania, just like Red ones. You don't need to collect the green crystal but it will unlock some secrets. Gold Crystals appear in Marble Saga, and have the same guidelines as Red crystals.