you need pHazers. substitute destroys you
Seconded. And a minor correction: Mega Heracross' multi-hit moves can bust through Substitutes, then strike the Pokemon behind them.
Anyway, Greninja needs the raw power of Hydro Pump over Scald's burn chance. It also needs Extrasensory to handle Mega Venusaur better (preferably over Dark Pulse)
Honestly, Meowstic isn't that good, making it a prime candidate to be taken out for a phazer, like Heatran:
-Lava Plume
-Toxic/Will-o-Wisp
-Protect
-Taunt/Roar/Stealth Rock
Nature: Calm
EVs: 248 HP/252 Def/8 SDef
Item: Leftovers
Skarmory:
-Roost
-Whirlwind
-Stealth Rock/Spikes/Brave Bird
-Defog/Brave Bird
Nature: Bold/Impish
EVs: 252 HP/252 Def/4 SDef or 252 HP/16 Def/240 SDef
Item: Leftovers/Rocky Helmet
Ability: Sturdy
Mega Heracross needs the raw power of Close Combat. Without it, it loses a lot of power; the defense drops can be eliminated by switching out. It only needs enough Speed to outspeed Bisharp:
-Pin Missile
-Close Combat
-Rock Blast
-Earthquake/Swords Dance
Nature: Adamant
EVs: 40 HP/252 Atk/216 Spe
Item: Heracronite
Ability: Guts/Moxie
Chandelure is outclassed by things like Charizard Y and Aegislash (for hitting harder), as well as Gengar (for being faster). Your Mega slot is taken, so Aegislash or Gengar will do:
Aegislash:
-Shadow Ball
-Shadow Sneak/Sacred Sword
-Iron Head/Sacred Sword/Pursuit
-King's Shield
Nature: Quiet
EVs: 244 HP/12 Def/252 SAtk
Item: Leftovers
or
-Substitute
-Shadow Ball
-Toxic
-King's Shield
Nature: Modest
EVs: 244 HP/12 Def/252 SAtk
Item: Leftovers
or
-Shadow Ball
-Shadow Sneak
-Flash Cannon/Sacred Sword
-Pursuit/Sacred Sword
Nature: Hasty/Naive
EVs: 4 Atk/252 SAtk/252 Spe
Item: Life Orb/Spooky Plate/Spell Tag
or
-Swords Dance
-Shadow Sneak
-Iron Head/Shadow Claw
-Sacred Sword/Head Smash
Nature: Adamant
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb
Gengar:
-Shadow Ball
-Sludge Bomb
-Focus Blast/Thunderbolt
-Destiny Bond
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb
or
-Substitute
-Shadow Ball
-Will-o-Wisp
-Disable/Taunt/Sludge Bomb/Sludge Wave/Focus Blast
Nature: Timid
EVs: 28 HP/148 SAtk/80 SDef/252 Spe
Item: Black Sludge
In OU, offensive Porygon2 is best off using Trick Room and not everyone on the team benefits from it. It's best off defensive, IMO:
-Ice Beam
-Thunderbolt
-Shadow Ball/Thunder Wave/Toxic
-Recover
Nature: Calm/Bold
EVs: 252 HP/4 Def/252 SDef (Calm) or 252 HP/252 Def/4 SDef (Bold)
Item: Eviolite
Ability: Trace
Shuckle's current set is too gimmicky. It's easily countered by Steel Pokemon, Poison Pokemon and those with Taunt. It also doesn't have time to execute the full strategy, due to OU's fast pace. However, Shuckle's best niche is a Sticky Web setter, which helps with Mega Heracross' so-so Speed:
-Sticky Web
-Stealth Rock
-Encore
-Infestation/Toxic/Knock Off
Nature: Bold/Impish
EVs: 248 HP/252 Def/8 SDef
Item: Mental Herb
Ability: Sturdy