Varios
When it completely fills and begins to flash, it means you can use the Orb Attack. Press the B button and your character will begin to glow and the whole screen looks somewhat blurry. In this state, your character's normal X or Y attacks become extremely powerful, often wiping out entire groups of enemies with ease. Your speed is also increased in this state. When the Orb Meter drops back down, you return to your original state and must begin collecting red orbs again to enter this state again. Whenever you kill enemies with the Orb Attack, they emit blue orbs, rather than red. They enter your character in the same way, and fill a secondary Orb Meter (it fills with the color blue, and is located near your red Orb Meter). When this blue Orb Meter is full press B and you can use the Orb Spark. This is a one-time attack that is ridiculously powerful and will generally kill every enemy nearby (the exception, of course, is bosses). The down side to this attack is that it takes a long time to fill the blue Orb Meter so you usually don't get to use the Orb Spark more