First of all, get rid of Toxic on Aegislash and put Shadow sneak in there. King's sheild+Shadow sneak is a common and good combo.
Next up, Put Rapid Spin on Forretress, as quickly as you can.
Then,you need 2 pokemon who can cover spore spammers so i suggest either Mega-Houndoom or Mega-Charizard X for the added dragon type.
Last but not least, you want something that can tank Fairies better that poison types and i would suggest Klefki OR Steelix.
And you don't need Crustle if you have Forretress...
So your team should be like that:
Aegislash
Ghost/Steel
Ability: Stance Change
Item: Leftovers
Moves
King's Shield
Shadow Sneak
Shadow Claw
Sacred Sword
Crobat
Poison/Flying
Ability: ???
Item: Black Sludge
Moves
Zen Headbutt
Confuse Ray
Fly
Poison Fang
Forretress
Bug/Steel
Ability: Sturdy
Item: ???
Moves
Rapid Spin
Toxic
Stealth Rock
Gyro Ball
Greninja
Water/Dark
Ability: Protean
Item: ???
Moves
Water Shuriken
Night Slash
Dig
Aerial Ace
Charizard
Ability: Blaze
Item: CharizarditeX
-Flare Blitz
-Dragon Claw
-Heat Wave
-Air Slash
Klefki
Ability: Magician
Item: (leave empty so magician can do its thing)
-Play Rough
-Heal Block
-Crafty Sheild (for spore spammers\Toxic spammers)
-Psychic
I don't agree with these set suggestions. Even though King's Shield sets are easily played around, they're viable nonetheless. Aegislash can also be played as a wallbreaker/offensive pivot:
-Shadow Ball
-Iron Head/Shadow Sneak
-Sacred Sword/Shadow Sneak
-King's Shield
Nature: Quiet
EVs: 240 HP/252 SAtk/4 SDef/12 Spe
Item: Leftovers
or
-Shadow Ball
-Shadow Sneak
-Sacred Sword
-Iron Head/King's Shield
Nature: Quiet
EVs: 252 Atk/252 SAtk/4 SDef
Item: Leftovers/Life Orb
or
-Swords Dance
-King's Shield/Shadow Claw
-Shadow Sneak
-Sacred Sword
Nature: Adamant
EVs: 240 HP/252 Atk/4 SDef/12 Spe
Item: Leftovers
or
-Swords Dance
-Autotomize
-Shadow Claw
-Sacred Sword
Nature: Adamant
EVs: 84 HP/252 Atk/4 SDef/168 Spe
Item: Leftovers
or
-Autotomize
-Shadow Ball
-Hidden Power (Ice)
-Sacred Sword/Iron Head/Flash Cannon
Nature: Rash/Modest
EVs: 88 Atk/252 SAtk/168 Spe
Item: Life Orb/Weakness Policy
Crobat is best played as an offensive stallbreaker/Defogger. Its offensive move pool is shallow and doesn't have good coverage together. Brave Bird is its only viable offensive option:
-Brave Bird
-Defog (clears away entry hazards and screens on both sides of the field)
-Roost
-Taunt/Toxic
Nature: Jolly
EVs: 168 HP/136 Atk/4 SDef/200 Spe
Item: Black Sludge
Ability: Infiltrator
Forretress is massive setup bait. While it may be a subpar option this generation for this reason alone, people still use it for the Rapid Spin and hazard support it provides:
-Stealth Rock/Spikes
-Rapid Spin
-Gyro Ball
-Earthquake/Volt Switch
Nature: Relaxed
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
Charizard X is supposed to use physical attacks only because of Tough Claws powering up its contact moves (which tend to be physical in nature). Leave special moves to Charizard Y:
-Dragon Dance
-Flare Blitz
-Dragon Claw
-Earthquake/Roost
Nature: Adamant/Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Charizardite X
Ability: Blaze
or
-Fire Punch
-Dragon Claw
-Will-o-Wisp
-Roost
Nature: Jolly
EVs: 248 HP/84 SDef/176 Spe
Item: Charizardite X
Ability: Blaze
Time and time again, I've always disapproved of physical Greninja. Its Attack isn't high enough to make the most out of its move pool, and its special moves hit harder:
-Hydro Pump/Surf
-Ice Beam/Dark Pulse
-Extrasensory/Dark Pulse
-U-turn/Hidden Power (Fire)
Nature: Hasty/Timid
EVs: 4 Atk/252 SAtk/252 Spe
Item: Life Orb
Ability: Protean
or
-Spikes
-Hydro Pump/Surf
-Ice Beam
-U-turn/Extrasensory
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb/Focus Sash
Prankster is the one and only ability Klefki should use because of its wide support move pool. Magician is absolutely useless in comparison:
-Reflect
-Light Screen
-Spikes
-Dazzling Gleam/Foul Play
Nature: Bold
EVs: 252 HP/152 Def/104 SDef
Item: Light Clay
Ability: Prankster