I have news for you PT mains.... the "batton pass" or "buffering" and attack while switching actually works pretty well, its not perfect, but its a goodthing to keep in mind, so ill post my findings
1. Every pokemon has an animation when it returns to its pokeball or comes out on the stages, and some of those frames are invicible (there are vulnerabilty frames on the last part of the coming out animation, that is one of the reasons the change is easily punished, you cannot control your pokemon until that animation finishes)
2. When your pokemon is on the "returning to its pokeball" animation you can input "any" attack (it havent worked with smashes or grabs, but my z button is bad, so i always try to shield-then-grab, and that does work), the pokemon returning to the pokeball wont do it, but the good thing is that the coming out pokemon will perform the attack cutting the comeout animation's time to something like the half.
3. When the animation finishes the pokemon is vulnerable, but able to do the attack you did input to the returning pokemon, that means you can get punished if your coming out attack:
*Is slow(rock smash does not work well when the oponent is near to punish you soon, but its great if they are far and runing to you to punish, then get rocksmashed)
*Is outprioritized(ikes charged fsmash still punishes squirtles ftilt out of pokeball, and it HURTS.... lol)
*Has a strange hitbox which allows te enemy to punish(vine whip)
*The very few knockback and laggy combination ( yeah im looking at you, razor leaf)
4. There are some moves wich are incredbly handy on this tecniche, to name some:
*Charizards utilt,dtilt,flamethrower,upb
*Ivysaurs dtilt,ftilt,utilt, and hell does bullet seed works wonders
*Squirtles utilt,dtilt,jab
5. You can also press x or y tojump out of the pokeball,nad go for an aerial
6. Its hard to smash, because of the little time to input an attack, and if you charge the smash some weird thing happens and it doesnt come out, i think smashes hardly will be usefull to prevent the punishing because of this
7. If you wanna learn to do it, do it with the ivysaur-to-charizard change, it works good because ivysaur has the most noticeable coming back animation( input the attack when you see the flower alone on the ground); and then move on learning the time to do it on the other changes.
Hope that helps every PT main out there :D
Sorry for no vid but i dont have any way to get one