If this is for competitive:
Charizard's Mega Evolutions are the sole reason why it's even used in the first place. Its regular form just doesn't cut it compared to them: Talonflame is a non-Mega Fire Pokemon to turn to:
-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
-Brave Bird
-Taunt
-Will-o-Wisp
-Roost
Nature: Careful
EVs: 248 HP/252 SDef/8 Spe
Item: Leftovers
Ability: Gale Wings
or
-Swords Dance
-Flare Blitz
-Brave Bird
-Natural Gift
Nature: Jolly
EVs: 120 HP/252 Atk/136 Spe
Item: Liechi Berry/Salac Berry
Ability: Gale Wings
Mega Kick doesn't give Swampert notable coverage, while Avalanche isn't that good, since it forces Swampert to go last. Mega Swampert should support itself using Rain Dance and Ice Punch should be used as a more reliable way to hit Grass Pokemon on the switch:
-Waterfall
-Earthquake
-Ice Punch
-Rain Dance
Nature: Adamant
EVs: 152 HP/252 Atk/104 Spe
Item: Swampertite
Alakazam appreciates the freedom of switching its moves freely, so Choice Specs isn't a good option on it. What good are Charge Beam's boosts when Alakazam is locked into said move? Given Alakazam's frailty, it should hold Focus Sash:
-Psychic
-Shadow Ball
-Focus Blast
-Hidden Power (Ice/Fire)/Thunder Wave/Encore
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Focus Sash
Ability: Magic Guard
Though Gengar is frail, it can easily force switches with Substitute. It can also act as an offensive utility Pokemon, but your current coverage moves for it aren't that good:
-Shadow Ball
-Sludge Wave/Sludge Bomb
-Focus Blast
-Destiny Bond/Taunt/Substitute
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb/Focus Sash/Black Sludge
or
-Substitute
-Shadow Ball
-Will-o-Wisp
-Taunt/Sludge Bomb/Sludge Wave/Disable
Nature: Timid
EVs: 28 HP/148 SAtk/80 SDef/252 Spe
Item: Black Sludge
or
-Hex
-Taunt
-Will-o-Wisp
-Sludge Wave/Sludge Bomb/Substitute
Nature: Timid
EVs: 8 HP/248 SAtk/252 Spe
Item: Black Sludge
Drapion and Electivire are outclassed in standard play because even though the latter has good coverage moves, it tends to get KOed in return if it fails to KO something. The former is outclassed by other Dark Pokemon with better utility like Mandibuzz.
That being said, the aforementioned Mandibuzz is better over Drapion, as it can use Defog to clear away Stealth Rock, the hazard that Talonflame loathes. Stealth Rock is pretty much a requirement in OU play, so Drapion should be replaced with stuff like Therian Landorus, Ferrothorn, Tyranitar, Terrakion, Empoleon or Heatran:
Mandibuzz:
-Foul Play
-Roost
-Defog
-Taunt/Whirlwind
Nature: Bold
EVs: 248 HP/136 Def/108 SDef/16 Spe
Item: Leftovers
Ability: Overcoat
Therian Landorus:
-Stealth Rock
-Earthquake
-U-turn
-Stone Edge/Knock Off/Rock Slide
Nature: Impish
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
Ferrothorn:
-Stealth Rock/Spikes
-Leech Seed
-Power Whip/Gyro Ball
-Gyro Ball/Protect/Thunder Wave
Nature: Relaxed
EVs: 252 HP/88 Def/168 SDef
Item: Leftovers/Shed Shell
Ability: Iron Barbs
Tyranitar:
-Stealth Rock
-Crunch/Pursuit
-Fire Blast
-Ice Beam/Rock Slide/Thunder Wave
Nature: Sassy
EVs: 248 HP/136 Def/124 SDef
Item: Leftovers
Ability: Sand Stream
Terrakion:
-Stealth Rock
-Stone Edge
-Close Combat
-Taunt/Swords Dance
Nature: Jolly
EVs: 252 SAtk/4 SDef/252 Spe
Item: Focus Sash/Life Orb
Empoleon:
-Stealth Rock
-Scald
-Defog
-Roar/Protect/Toxic
Nature: Calm
EVs: 248 HP/8 Def/252 SDef
Item: Leftovers
Ability: Torrent
Heatran:
-Stealth Rock
-Lava Plume
-Toxic
-Taunt/Earth Power/Roar
Nature: Calm
EVs: 248 HP/192 SDef/68 Spe
Item: Leftovers
