The sonic rain boom is impossible for a living being to pull off by its own. You can't just go 5 times the speed of sound without breaking your wings and falling to your death. If you have a plane or something protecting you from dieing like a fighter jet. You need oxygen to survive that height and speed and rainbow dash doesn't and how would you be able to do the rainbow part too that is totally impossible in real life. I do like rainbow dash I'm no hater but it is the truth. But it's just a theory, a pony theory!