My brief experience with marth:
*Dancing blade is much much more consistent
*down throw combos are much more consistent. In training mode, i was able to down throw> tipper up air captain falcon and kill him, with it registering as a true combo. That *definitely* wasn't doable before
*forward throw combos are also more consistent. Before, SH shieldbreaker true comobed from forward throw, but with the patch, it's much easier to land and do at higher percents (not saying this is a good option, just making a point).
* They definitely changed dair. Personally, I dont feel any change in regards to lag as some others have mentioned. However, I feel like the spiking hitbox is out a bit longer. Before, only right below him spiked, but now, it spikes a bit in front of him as well (I was actually able to stand right in front of cptain falcon and Sh dair and get a spike. And that's without drifting at all). Also, before the patch, if someone regrabed the ledge and you were right by it, you could only Sh dair into the ledge and get it to spike with your back turned. Now, I can get it to spike regardless of which way marth faces. Probably due to the spiking hitbox being out a bit longer, which now allows it to spike a bit in front of him and not just simply under him.
There may be more stuff, but thats all i recognized within30 minutes