For those wondering, the current charge mechanic is shared amongst all attacks. You start with 0 "charge". Each time you click an attack button (regardless if it lets you attack or not) you gain 1 charge. If you have enough charge, the attack triggers and you're deducted its "charge" cost.

Throwing Star = +1, Cost 0

Shooting Star = +1, Cost 2

Blasting Star = +1, Cost 3

Exploding Star = +1, Cost 4