Here's my suggestions on it
On Greninja, go with choice specs and drop extrasensory for water shuriken. It's one goal is to sweep entire teams with shuriken. Since you have Kyurem, drop ice beam and replace it with spikes. This way, whenever you're sure your opponent will switch, drop some spikes to punish further switch ins and to make it easier to activate battle bond. Also change nature to timid to increase speed. Final set would be
Greninja-Ash @ Choice Specs
Ability: Battle Bond
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Spikes
- Dark Pulse
- Hydro Pump
- Water Shuriken
On Pelipper, replace hurricane with defog. You have no method of removing hazards and toxic spikes or stealth rock would ruin your team greatly. Everything else is okay
Swampert seems okay to me as well. Just consider using substitute over superpower but that's up to you
On Kyurem, replace power herb with the ice z crystal. A z freeze shock is gonna hurt a lot more than a regular freeze shock plus the z crystal does the same job of the power herb, only better. I'm not a fan of outrage since in gen seven, there are so many fairies running around and getting locked into outrage is a complete and utter death sentence. I would suggest this Kyurem set instead
Kyurem-Black @ Icium Z
Ability: Teravolt
EVs: 252 Atk / 4 SpA / 252 Spe
Naive Nature
- Ice Beam
- Substitute
- Fusion Bolt
- Freeze Shock
Remove Kartana. You already have Greninja, Swampert and Kyurem for wallbreaking and sweeping. Instead I would suggest replacing it with Ferrothorn with this set
Ferrothorn @ Leftovers
Ability: Iron Barbs
EVs: 248 HP / 80 Def / 180 SpD
Careful Nature
- Protect
- Gyro Ball
- Leech Seed
- Stealth Rock
I don't think Heatran is that good of a choice in rain since it's immune to fire anyway and the rain would just hamper with its own fire moves. Instead, I would suggest using Tornadus instead
Tornadus-Therian @ Rocky Helmet
Ability: Regenerator
EVs: 252 HP / 4 Def / 252 Spe
Timid Nature
- Defog
- U-turn
- Hurricane
- Knock Off
Tornadus is one of the best abusers of rain as it will finally have a stab that will hit its target. This set also comes with the benefit of easing prediction since it can usually take one strong move, provided stealth rock isn't on your side of the field. It's also one of the best, if not the best defogger in gen seven ou. While Pelipper has defog, you do not want to put it in too much risk
Here's a sample final team
https://pokepast.es/2983da013929f28a
