Basically how this works is you dash and then pivot the other direction and you should see your character do their pivot / turn around animation. Keep holding that direction for a second and then you can d.smash, f.smash, u.smash, or any move you want and they will retain the momentum of the pivot allowing you to do things like sliding up smashes with squirtle, sliding forward or down smash with MK, among many other cool things. This also allows you to cancel your run into ANY move, not just dash attack or up smash, so you can do something like run up pivot away from the person and then down smash. I’ve been doing this with MK and it’s pretty nice since the back hit on his down smash is his best KO move. You can also mix it up and just press grab and towards them and they’ll turn around and do a dash grab out of the pivot, so you get some mix ups out of it.
Best use I’ve seen for this is kinda like old wavedashing though. If someone approaches, run away from them and immediately pivot back towards them and punish with a down smash or whatever. Since you’re sliding it really helps with spacing and you can cause people to whiff things.
Also you can cancel your pivot back in the direction you were coming from, so you can rapidly pivot and move away from someone by something something like run away from the person, pivot towards them, immediately cancel back away from them, pivot towards them, lather rinse repeat. It’ll let you whip out a sliding move whenever you need it.
Overall, it’s one of the more useful ATs I’ve seen discovered.