Charizard Y generally needs a team built around it for it to excel.
Check out this post for reference.
Remember that Aegislash recently got banned to Ubers, so people might complain about you using it in Wi-Fi teams (Battle Spot is okay, though).
Mega Pinsir generally has to be Jolly simply because 105 Speed is rather good:
-Swords Dance
-Return
-Close Combat/Earthquake
-Quick Attack
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Pinsirite
Ability: Hyper Cutter/Mold Breaker
Teammates that work well with Mega Pinsir are Rapid Spinners and Defoggers because they get rid of Stealth Rock. Here they are:
Mandibuzz:
-Foul Play
-Roost
-Taunt/Whirlwind
-Defog
Nature: Bold
EVs: 248 HP/136 Def/108 SDef/16 Spe
Item: Leftovers
Ability: Overcoat
Excadrill:
-Earthquake
-Iron Head
-Rapid Spin
-Rock Slide/Stealth Rock
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Leftovers/Air Balloon
Ability: Mold Breaker
or
-Earthquake
-Iron Head
-Rock Slide
-Rapid Spin
Nature: Adamant/Jolly
EVs: 252 Atk/4 Def/252 Spe (Choice Scarf) or 120 HP/136 Atk/252 SDef (Assault Vest; Adamant only)
Item: Choice Scarf/Assault Vest
Ability: Mold Breaker
Starmie:
-Hydro Pump
-Psyshock/Thunderbolt
-Ice Beam
-Rapid Spin
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb/Leftovers
Ability: Natural Cure/Analytic
or
-Scald
-Rapid Spin
-Reflect Type
-Recover
Nature: Timid
EVs: 252 HP/32 Def/224 Spe
Item: Leftovers
Ability: Natural Cure
Latias:
-Draco Meteor
-Psyshock/Thunderbolt/Hidden Power (Fire)
-Defog
-Healing Wish/Roost/Recover
Nature: Timid
EVs: 72 HP/184 SAtk/252 Spe
Item: Life Orb/Leftovers
Latios:
-Draco Meteor
-Psyshock
-Thunderbolt/Hidden Power (Fire)/Earthquake
-Defog
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb
Mega Pinsir works best with other Flying Pokemon such as Talonflame and Staraptor, since they wear down each other's checks/counters up to the point that one of them can clean up freely:
Talonflame:
Talonflame:
-Swords Dance
-Flare Blitz
-Brave Bird
-Roost
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb/Sharp Beak/Sky Plate
Ability: Gale Wings
or
-Flare Blitz
-Brave Bird
-U-turn
-Tailwind/Roost
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Band/Sharp Beak/Sky Plate
Ability: Gale Wings
or
-Bulk Up
-Brave Bird
-Roost
-Taunt/Will-o-Wisp
Nature: Careful
EVs: 248 HP/8 Def/252 SDef
Item: Leftovers
Ability: Gale Wings
or
-Swords Dance
-Flare Blitz
-Brave Bird
-Natural Gift
Nature: Jolly
EVs: 80 HP/252 Atk/176 Spe
Item: Liechi Berry/Salac Berry
Ability: Gale Wings
or
-Brave Bird
-Taunt
-Will-o-Wisp
-Roost
Nature: Careful
EVs: 248 HP/252 SDef/8 Spe
Item: Leftovers
Ability: Gale Wings
Staraptor:
-Double-Edge
-Brave Bird
-Close Combat
-U-turn/Final Gambit/Quick Attack
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Scarf/Choice Band
Ability: Reckless
Electric Pokemon pair well with Pinsir to deal with opposing Flying Pokemon. These include Magnezone, Thundurus, Raikou and Wash Rotom:
Magnzone:
-Thunderbolt
-Volt Switch
-Flash Cannon
-Hidden Power (Fire)
Nature: Modest/Timid
EVs: 172 HP/252 SAtk/84 Spe (Modest) or 4 HP/252 SAtk/252 Spe (Timid)
Item: Choice Specs (Modest)/Choice Scarf (Timid)
Ability: Magnet Pull
or
-Magnet Rise
-Thunderbolt
-Flash Cannon
-Hidden Power (Fire)
Nature: Modest
EVs: 128 HP/252 SAtk/128 Spe
Item: Air Balloon
Ability: Magnet Pull
Thundurus:
-Thunderbolt
-Hidden Power (Ice)
-Psychic/Focus Blast
-Thunder Wave
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Life Orb/Leftovers
Ability: Prankster
or
-Nasty Plot
-Thunderbolt
-Hidden Power (Flying/Ice)
-Substitute/Focus Blast/Psychic
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Leftovers/Life Orb
Ability: Prankster
or
-Thunderbolt
-Knock Off
-Superpower/Thunder Wave
-Hidden Power (Ice)
Nature: Hasty/Naive
EVs: 76 Atk/180 SAtk/252 Spe
Item: Life Orb
Wash Rotom:
-Volt Switch
-Hydro Pump
-Will-o-Wisp
-Pain Split/Rest
Nature: Bold/Calm
EVs: 248 HP/216 Def/44 Spe (Bold) or 248 HP/216 SDef/44 Spe (Calm)
Item: Leftovers/Chesto Berry
or
-Volt Switch
-Hydro Pump
-Hidden Power (Ice)/Will-o-Wisp
-Trick
Nature: Modest/Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Choice Scarf
This is just an example team; I'll have to give feedback to the rest of your proposed team members.
Infernape is best mixed, not physical. It also has to be Hasty/Naive:
-Flare Blitz/Fire Blast
-Close Combat
-Grass Knot/Stone Edge/Thunder Punch
-Mach Punch/Hidden Power (Ice)/U-turn/Thunder Punch
Nature: Hasty/Naive
EVs: 168 Atk/88 SAtk/252 Spe
Item: Life Orb
Ferrothorn has to be a Stealth Rock setter; it can go to the Mega Pinsir team I suggested:
-Stealth Rock
-Leech Seed
-Power Whip
-Gyro Ball/Thunder Wave/Knock Off/Protect
Nature: Relaxed
EVs: 252 HP/88 Def/168 SDef
Item: Leftovers
Ability: Iron Barbs
Out of your listed Pokemon, Metagross and Ambipom aren't viable. The former's susceptibility to Knock Off really hurt it; the latter is outclassed by faster attackers like Greninja.
