Items would be appreciated, but if you choose to use Mega Pokemon, use 1 only.
Infernape can go mixed, you know. Poison Jab doesn't give it noteworthy coverage apart from Fairies, which are hit hard by Flare Blitz already. Speaking of Flare Blitz, it's stronger than Iron Fist-boosted Fire Punch:
-Overheat/Fire Blast
-Close Combat
-Thunder Punch
-U-turn/Mach Punch/Stone Edge
Nature: Hasty/Naive
EVs: 252 Atk/4 SAtk/252 Spe
Item: Life Orb/Expert Belt
Ability: Iron Fist
or
-Flare Blitz
-Close Combat
-U-turn
-Thunder Punch/Mach Punch
Nature: Jolly
EVs: 252 Atk/4 SDef/252 Spe
Item: Choice Band
Ability: Iron Fist
or
-Fake Out
-Stealth Rock
-Overheat
-Close Combat
Nature: Hasty/Naive
EVs: 252 Atk/4 SAtk/252 Spe
Item: Focus Sash
Ability: Blaze
or
-Fire Blast/Flare Blitz
-Close Combat
-U-turn
-Hidden Power (Ice)/Stone Edge/Thunder Punch
Nature: Hasty/Naive
EVs: 36 Atk/220 SAtk/252 Spe
Item: Choice Scarf
Ability: Blaze
Never use Fly competitively, as it's too easily played around. Hydreigon is also one of the best wall breakers out there:
-Draco Meteor
-Dark Pulse
-Iron Tail/Superpower/Flash Cannon
-Fire Blast/Roost
Nature: Mild/Rash/Modest
EVs: 40 HP/236 SAtk/232 Spe
Item: Life Orb
or
-Draco Meteor
-Dark Pulse
-Flash Cannon/Focus Blast
-Fire Blast/Earth Power
Nature: Modest
EVs: 24 HP/252 SAtk/232 Spe
Item: Choice Specs
Tyranitar should only use max Speed when it's using Dragon Dance or Choice Scarf. Without either of those, it should use a bulky spread:
-Stone Edge/Rock Slide
-Crunch
-Pursuit
-Stealth Rock/Fire Blast
Nature: Careful/Sassy
EVs: 252 HP/4 Atk/252 SDef
Item: Leftovers/Assault Vest
Ability: Sand Stream
or
-Stone Edge
-Crunch
-Pursuit
-Earthquake/Ice Punch
Nature: Adamant/Jolly
EVs: 180 HP/252 Atk/76 Spe (Adamant) or 4 HP/252 Atk/252 Spe
Item: Choice Band (Adamant)/Choice Scarf (Jolly)
Ability: Sand Stream
or
-Dragon Dance
-Stone Edge
-Crunch
-Earthquake/Ice Punch
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Tyranitarite
Ability: Sand Stream
Metagross is best played as an Assault Vest user or bulky support:
-Stealth Rock
-Meteor Mash
-Earthquake
-Bullet Punch/Pursuit/Trick
Nature: Adamant
EVs: 252 HP/252 Atk/4 Def
Item: Leftovers/Iron Ball
Ability: Clear Body
or
-Meteor Mash
-Earthquake
-Bullet Punch
-Zen Headbutt/Pursuit
Nature: Adamant
EVs: 252 HP/252 Atk/4 Def
Item: Assault Vest
Ability: Clear Body
Supereffective Iron Head does a little more than a neutral STAB Earthquake. To me, this isn't worth it, as Earthquake hits Fairies hard enough already; Garchomp has no need for Iron Head as a result:
-Swords Dance
-Outrage/Dragon Claw
-Earthquake
-Stone Edge/Fire Fang
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Lum Berry/Yache Berry/Garchompite
or
-Outrage
-Earthquake
-Stone Edge/Fire Fang/Fire Blast
-Dragon Claw/Dual Chop
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Choice Band/Choice Scarf
or
-Stealth Rock
-Outrage/Dragon Claw
-Earthquake
-Fire Blast/Swords Dance
Nature: Naive/Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Lum Berry/Focus Sash
or
-Draco Meteor
-Earthquake
-Stone Edge
-Fire Blast
Nature: Naughty
EVs: 224 Atk/32 SAtk/252 Spe
Item: Garchompite
I'll assume that you have a hard time giving Gyarados its other two moves:
-Dragon Dance
-Waterfall
-Earthquake
-Bite/Stone Edge/Substitute
Nature: Adamant
EVs: 32 HP/252 Atk/224 Spe
Item: Gyaradosite
Ability: Intimidate
or
-Substitute/Taunt
-Dragon Dance
-Waterfall
-Bounce/Earthquake
Nature: Adamant
EVs: 120 HP/64 Atk/100 Def/224 Spe
Item: Leftovers
Ability: Intimidate
or
-Dragon Dance
-Waterfall
-Earthquake
-Stone Edge/Bounce
Nature: Adamant/Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Lum Berry
or
-Rest
-Sleep Talk
-Waterfall
-Roar/Dragon Tail
Nature: Impish
EVs: 248 HP/252 Def/8 SDef
Item: Leftovers
Ability: Intimidate
If you want to replace Hydreigon, I'd suggest a Fighting-resistant Pokemon like your own Fairy Pokemon because of how vulnerable to Fighting this team is. Azumarill or Sylveon are good candidates:
Azumarill:
-Waterfall
-Aqua Jet
-Play Rough
-Superpower
Nature: Adamant
EVs: 212 HP/252 Atk/44 Spe
Item: Choice Band
Ability: Huge Power
or
-Belly Drum
-Aqua Jet
-Play Rough
-Waterfall/Superpower
Nature: Adamant
EVs: 92 HP/252 Atk/164 Spe
Item: Sitrus Berry
Ability: Huge Power
or
-Aqua Jet
-Play Rough
-Power-Up Punch
-Waterfall/Knock Off
Nature: Adamant
EVs: 16 HP/252 Atk/240 SDef
Item: Assault Vest
Ability: Huge Power
Sylveon:
-Wish
-Protect
-Hyper Voice
-Heal Bell
Nature: Bold
EVs: 244 HP/252 Def/12 Spe
Item: Leftovers
Ability: Pixilate
or
-Hyper Voice
-Shadow Ball
-Psyshock
-Hidden Power (Fire)
Nature: Modest
EVs: 244 HP/252 SAtk/12 Spe
Item: Choice Specs
Ability: Pixilate