Attack Changes
There are two things here that aren't easily visible. GIF is slowed down to 1/3 speed during the new Back Airs.
One of the changes is a new Back Air. Lucario does it twice in the GIF. The first time is right at the beginning. The second time is on Luigi getting a KO. This new Back Air seems to have more start up lag (and a new animation), but seems to have more power as a trade off.
I was trying this out in Brawl with the same damage percentage for Luigi and Lucario and making Lucario use its Back Air. It was not a KO when Luigi was standing on the left part of the center diamond on Final Destination. It was pretty bad. Though Lucario does get an aura buff in Smash 4, it still should have killed Luigi easily at that percentage in Brawl. It also required a sweet spot in Brawl which made it really bad to use.
The other change is a faster Forward Air. You can easily miss it since it happens only for a short period of time. It happens right before Lucario does the Back Air on Luigi. That's a welcome change.