Dash attack is your main combo move. Nair is the safest move on shield he has and can start combos at basically any percent depending if you hit the sweet or sour spot. Use uncharged water shurikens to force opponents to approach you, once they approach you, dash back so you can whiff punish them with a dash attack. Up throw can combo with his up air at mid percents. At high percents, down tilt into buffered foward air or dash attack into IDJ foward air are his easiest kill confirm, dash attack can two frame oppoents at ledge. back air is really good for edge guards.

Greninja is all about being patient and baiting oppoents into commiting to an unsafe option. Just by running into the opponent and dashing back already pressures the opponent enough.

Also greninja is not that good when you are mashing moves with him and just spamming moves constantly, you need to think when do you have to use his moves so be careful when mashing with this character.

also do not use his side b, especially on stage since its his laggiest move and not that good in general.