These trick serves only work once or twice a match vs a good player. I have a serve where I swing and completely miss the ball, then slice under the ball before it hits the ground, basically hitting a drop shot serve with tons of sidespin. However, its not a serve I would do more than once or twice, if ever against someone good, because if they read it then itll get killed.
Mansour Bahrami has that same serve. He still does it on the Senior Circuit. I would freak if someone served to me like that!