Better mob projectiles

I am making a mod actually not really im only at the planning stage but my mod Will have boss Mobs but the projectiles are not best Its there sould be a easy way to give delay to the projectile no matter how long the draw back speed is It just spams it non stop there sould also be an easy way to give conditions the projectiles and mob invinsible to certan projectile Easly

Also why is there no way to give the projectile no gravity without using procedures