At 13, you don't need to throw any breaking pitches that put stress on your elbow. Stick with the fastball and change, and hone your skills at hitting spots. Try middle relief to start, but as I said, practice hitting certain spots. Your control and placement of each pitch will win you games, not a bunch of fancy pitches that will damage your elbow. You want to still be able to get people out 5 years from now. Start working on a slow curve at 15, slider and sharp curve at 16. A sinking fastball at 16 1/2, depending on how you grow, will turn into your money pitch, but you need a strong elbow to throw it. NEVER, EVER, OVERTHROW !!