Greninja pretty much needs Gunk Shot nowadays because that attack has the ability to let it deal with Fairy Pokemon, a type that Greninja struggled against in X/Y (to be more specific, Greninja's strongest attack against them at that point was Hydro Pump, and Fairies could easily shrug it off and retaliate). And speaking of Hydro Pump, if Greninja must use a Water STAB, the former should be used because Greninja is too frail to rely on the burn rate and the extra power is appreciated. Low Kick is also an option over the Water STAB to let Greninja hit Tyranitar and Heatran more reliably:
-Hydro Pump/Low Kick
-Ice Beam
-Gunk Shot
-Dark Pulse/Grass Knot/Hidden Power (Fire)/Extrasensory
Nature: Naive
EVs: 40 Atk/216 SAtk/252 Spe
Item: Lfie Orb
Ability: Protean
Better Talonflame sets below. Bulky Talonflame can get away with dropping Flare Blitz to make some attackers setup bait or to stallbreak:
-Swords Dance
-Flare Blitz
-Brave Bird/Acrobatics
-Roost
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Sharp Beak/Sky Plate/none
Ability: Gale Wings
or
-Swords Dance
-Brave Bird/Acrobatics
-Taunt/Will-o-Wisp
-Roost
Nature: Adamant
EVs: 248 HP/252 Atk/8 Spe
Item: Leftovers/none
Ability: Gale Wings
or
-Flare Blitz
-Brave Bird
-U-turn
-Steel Wing/Tailwind
Nature: Adamant/Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Band
Ability: Gale Wings
or
-Brave Bird/Acrobatics
-Bulk Up/Taunt
-Will-o-Wisp/Taunt
-Roost
Nature: Careful
EVs: 248 HP/252 SDef/8 Spe
Item: Leftovers/none
Ability: Gale Wings
If you want to use Heal Bell on Clefable, drop Flamethrower. Have other teammates handle Steel Pokemon if you plan on using Clefable. A Calm nature with 252 HP/172 Def/84 SDef, as weird as this sounds, allows Clefable to avoid the 2HKO from things like Thundurus' Thunderbolt and Jolly Mega Gyarados' Waterfall pre-Calm Mind.
Mega Kangaskhan does Power-Up Punch abuse much better because of Parental Bond. Snorlax is better off using:
-Return/Body Slam
-Earthquake
-Pursuit/Crunch
-Fire Punch/Crunch
Nature: Adamant
EVs: 252 Atk/252 Def/4 SDef
Item: Assault Vest
Ability: Thick Fat
Mega Tyranitar faces stiff competition from Mega Altaria, Mega Gyarados, and Mega Charizard X as a Dragon Dancer because even though Mega Tyranitar is very bulky, its common weaknesses (7 in fact) make this kind of problematic. You could make Mega Tyranitar work if your Mega slot isn't taken up:
-Stone Edge
-Crunch/Ice Punch
-Pursuit
-Superpower
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe (Jolly) or 100 HP/252 Atk/156 Spe (Adamant)
Item: Choice Scarf (Jolly)/Choice Band (Adamant)
Ability: Sand Stream
or
-Stealth Rock
-Stone Edge
-Crunch/Ice Beam/Fire Blast
-Pursuit
Nature: Relaxed
EVs: 248 HP/80 Def/180 SDef
Item: Smooth Rock
Ability: Sand Stream
or
-Dragon Dance
-Stone Edge
-Crunch/Ice Punch
-Superpower/Fire Punch
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Tyranitarite
Ability: Sand Stream
As for the team, I'd pick Tyranitar, Excadrill (use the Sand Rush variant with an Adamant nature), Talonflame, Poison Heal Breloom (you'll need to re-breed, though; it's better than Focus Sash Technician Breloom because Focus Sash will be broken in sandstorm, and if it gets used up during sandstorm, Breloom will be KOed after it attacks), Clefable (note that Moonlight's recovery will be hindered in sand), and Greninja.
Here's Poison Heal Breloom if you're interested:
-Swords Dance
-Seed Bomb
-Superpower/Drain Punch
-Facade/Mach Punch
Nature: Jolly
EVs: 12 HP/244 Atk/252 Spe
Item: Toxic Orb
Ability: Poison Heal