in terms of reveals, I'd say the most hype for me was either
or
Pac-Man was one of the first 3rd parties that came to mind for me as a potential Smash candidate, after Sonic and Snake were in Brawl. I pretty much screamed when he got confirmed. That being said, it would've been a lot more hype if they showed off his trailer at the actual E3 presentation instead of a random Developer's Conference. They definitely could've swapped Pac-Man and Palutena's reveals around. That, and with Bandai Namco developing 4, it was really only a matter of time.
As for Greninja, Froakie was my starter in X&Y and grew such an attachment to it. It and it's evolutions have gone to become some of my favorite Pokemon of all time, especially Greninja in particular. Fast forward to the April Smash Direct, where I too was expecting the silhouette to be Mewtwo. Much to my delight, it was my froggy boi.
Quick honorable mention to
who was in a similar boat as Greninja, and would've been legitimately hype if he wasn't already leaked to the moon and back.