It's nearly impossible to make new projectiles. The only way to do it is to change already existing projectiles, such as Mario's fireball. But if you're using a PSA of a character that doesn't have any projectiles, then you're out of luck.

Ok then, how could I modify projectiles?

Hello!
I'm looking to make a psa with a projectile but im not sure how to make a projectile.
Can anyone help?
Thanks.