Six Pokemon are required and while legendaries can be suggested, do remember that many people do not like using them because of how easy it makes the game. You might also want to keep the starter.
- Moves are required for each Pokemon.
Greninja @ Mystic Water/ Black Glasses
-Extrasensory/ Ice Beam
-Dark Pulse/ Night Slash
Why is his tongue a scarf? The foam he had as a Froakie/ Frogadier would be so much cooler.
Dark Pulse or Night Slash, whichever's easier for you. Greninja can be a good mixed Pokemon in-game. Water Shuriken is actually more useful than you'd think, because of those Gravelers
and Boldres; Water Shurkien will break Sturdy. Either Extrasensory for Fighting coverage or Ice Beam for Grass coverage, so it would depend on the rest of the team. Or you can sacrifice Water Shuriken for one or the other. Considering that I'm advising Venusaur, I think Extrasensory is more beneficial, because Venusaur can handle grass types.
Acrobatics is another moveset option, if you so felt like it. It'll most likely OHKO Chestnaught if you're a few levels above it.
Greninja is a really solid starter; great speed, decent attacks and some nice STAB moves.
Weak to: Electric, Grass, Bug, Fighting, Fairy
Resists: Water, Fire, Steel, Ice, Dark, Ghost
Immune to: Psychic
Venusaur @ Miracle Seed/ Poison Barb