Good build. Since Greninja always nullifies buffs at a fixed time it's best to wait before setting up. I also agree with other user's suggestion of terrain/leftovers, you'll need less turns to attack, which means less chance of getting crit or missing since Gren's evade is quite high by that point.

How on earth is this guide supposed to work when half way thru Cinderace nullifies all your buffs rendering your attack power back to square one?

ez soloing.. life orb recommended.

Had no problem soloing it with this guide, though I made some slight adjustments. Replaced Slack off with psychic terrain and used leftovers as a held item.

0/10 so far using this guide. Do not recommend it to anyone.

Why punching glove for the item, stored power isn't a punch move? Aren't life orb or sitrus berry preferred?

Why does it list punching gloves as its held item?

I think you made a mistake here. It says raise IV except for Sp Atk and Agility. I think you mean Sp Def and Speed. The only attack it learns is a special attack so it doesn’t make sense to not increase that.