HP can still edgeguard some recoveries very reliably. It`s extremely effective against purely vertical recoveries like Ike`s Up B or for hitting Ness to push him away from his PK Thunder. It`s a lot weaker than before so you won`t be able to gimp everyone with it, but even if you don`t you usually send them above you in helpless state right into range of your sweetspot Usmash. So it`s still worth using every time you expect them to Up B.
Also to prevent getting shield grabbed when approaching with short hop fast fall Nairs, always follow up the Nair with a Jab if they shield. The Jab comes out before their grab, so if they try to shield grab, you`ll hit them for 10% free damage.
A good combo which you can do with Water Shuriken is to fully charge one, then chase after it and if your opponent gets caught in it, you can hit them with Usmash or grab them. The combo into Usmash only works at low % (below 20%), but the charged WS -> grab combo works at all %.
Greninja has a lot of different combos. Shack already listed most of the reliable ones. I`d just add:
Dash Attack -> Fair
Nair -> Usmash
Also Uthrow -> Usmash/Utilt and Dtilt -> Dash Attack do not truly combo, but you can often land them if the opponent does not react quickly enough.
For more details about Greninja`s combos, you can check out this thread:
http://smashboards.com/threads/greninjas-true-combos.375003/
And here are some kill combos you can use. The % are against Sheik without rage on FD.
- sourspot Nair -> Usmash at 83-100%
- Dtilt -> hyphen Usmash at 83-120%
- Utilt -> Uair at 100-160%
- Dash Attack -> Fair at 100-140%
- Dtilt -> Uair at 130-320%
- Dtilt -> Fair at 132-300%
- Uthrow above 160%
- and Bthrow -> Bair -> Bair can gimp almost all characters at 0% if you Bthrow them off the ledge.