Bet this one's new: Greninja vs Mii Gunner
https://www.youtube.com/watch?v=8cqUurvh0bM
That was a good first stock.
Honestly, against zoners, I just run up and shield to wade through their projectiles. I don't immediately attack, but I like to just hang around in their personal space as long as I can, occasionally throwing out ftilts, multi jabs, or dtilts. I do this just to watch how they respond to someone being up close to them.
If they roll or spot dodge alot (usually the case with zoners, since they generally have a poor footsie game), I use jabs, u tilts, dsmashes and usmashes (the last two for punishing rolls). After I got enough damage on them, I'll start trying to do a little zoning of my own with a fully charged water shuriken (the priority on this move is pretty good) to get additional damage and pester them into coming after me.
Once they start charging me with dash attacks, run up grabs, and aggressive rolls (seriously), I switch to using shield and substitute. I also like to activate shadow sneak and make it look like I'm walking away in the other direction, only to teleport and KO them.
On a side note, Greninja's aerial approaches are kind of poor due to their landing lag and startup (doesn't help either that his short hop is so freakin high). Although there may be some potential in well spaced back airs for approaching.
Anyway, hoped this helped somebody!