A Charge Missile, aka a "char-ile" (but we all just say Charlie) is essentially just a quick charged beam shot followed by a missile. It sounds simple, but it requires a lot of practice in order to consistently pull it off and aim at your target. It is mainly done to reduce the number of missiles used and increase damage per second to defeat some bosses faster.
The first step to doing a Charlie is to do a quick charge shot. There are a few ways of doing it, but we are interested in the spin jump quick charge as that allows for faster aiming.
You will need to delay a bit after the charge shot in order for the missile to shoot properly, otherwise you may only shoot the charge beam. In order to do another Charlie, you will need to touch the ground and repeat the process. The timing is somewhat strict, but you will eventually get a feel for it.
charlie.mp4
It is recommended to first learn how to fire Quick Charge beams until you become used to how to aim with it in all directions and while moving.
Once you have learned that:
Can shave off seconds on certain bosses in Boss Rush mode and save on missiles in Survival Rush mode.