To be honest, after labbing it out, I don't think Greninja is a good character. I decided to mess around with his move angles to find out how DI works against him and a lot of his "combos" don't connect properly on a majority of the cast. The biggest example is his footstool combos, most characters have enough drift to evade the down aerial before it even lands, taking away one of his biggest tools. It's also possible to SDI his U-Smash so it functions like a Battlefield platform, making the second hit miss entirely. The same thing can be done to escape his U-Air before it finishes, and also avoids the semi-spike.
His frame data is pretty subpar, too. A lot of his moves aren't actually safe on shield unless perfectly spaced, which is hard to do because "perfectly spaced" for Greninja actually suffers from some Z-Axis issues on a couple moves (F-Air, B-Air, F-Tilt, etc). As already known, his OoS options and standing grab are atrocious, too, so he can't really utilize one of the best options in Smash 4 either.
I'm not entirely sure why this character is considered good at all.