Technicially, Charizard doesn't count for mono-Dragon, as its regular form is Fire/Flying. It's only Fire/Dragon when Mega Evolved, which is temporary.
Anyway:
What does Shadow Claw even hit outside of Hoopa Confined? A STAB neutral Flare Blitz outdamages a 2x super effective Shadow Claw. Speaking of Flare Blitz, its extra power is worth the recoil, and said recoil can be healed with Roost. Also, put the last 4 EVs into either defensive stat, as putting them in HP will make Charizard's HP even, meaning it will get KOed by 2 Stealth Rock switch ins while in regular form:
-Dragon Dance
-Flare Blitz
-Dragon Claw
-Roost
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Charizardite X
Ability: Blaze
Critdra /could/ work, but it has a bad tendency to get badly screwed over by offensive teams, which can outspeed it rather easily. In the end, Kingdra is better off on rain teams. Hydreigon is a better wall breaker that doesn't need setting up to be effective:
-Dark Pulse
-Draco Meteor
-Flash Cannon
-Superpower/Earth Power
Nature: Mild/Modest
EVs: 4 Atk/252 SAtk/252 Spe
Item: Life Orb
or
-Dark Pulse
-Draco Meteor
-U-turn
-Earth Power
Nature: Modest/Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb
Latios is better off as an all-out attacker. Magic Coat takes prediction to use, and Shadow Ball doesn't let it hit anything noteworthy, as Draco Meteor still outdamages a 2x super effective Shadow Ball:
-Draco Meteor
-Psyshock
-Hidden Power (Fire)/Roost/Recover/Earthquake
-Defog/Roost/Recover
Nature: Timid/Hasty
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb
or
-Calm Mind
-Draco Meteor
-Psyshock
-Recover/Roost/Surf
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Life Orb
or
-Draco Meteor
-Psyshock
-Hidden Power (Fire)/Defog
-Trick
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb
Apart from Gyarados, Thunderbolt doesn't let Dragalge hit anything else. Also, Sludge Wave > Sludge Bomb, so Dragalge can hit the occasional Bulletproof Chesnaught without having to resort to Draco Meteor. The main coverage moves Dragalge uses are Focus Blast and Scald to hit Heatran harder:
-Sludge Wave
-Draco Meteor
-Focus Blast/Hidden Power (Fire)
-Toxic Spikes/Scald
Nature: Modest
EVs: 228 HP/252 SAtk/28 Spe
Item: Black Sludge/Draco Plate/Dragon Fang/Choice Specs
Ability: Adaptability
or
-Toxic Spikes
-Sludge Wave
-Draco Meteor/Dragon Pulse
-Scald
Nature: Calm
EVs: 248 HP/232 SDef/28 Spe
Item: Black Sludge
Ability: Adaptability
Hone Claws is a waste of a moveslot on bulky Garchomp. It doesn't have the Attack investment to make the most out of the boost; that, and Hone Claws provides a smaller Attack boost than Swords Dance, and Dragon Tail is already decently accurate:
-Stealth Rock
-Dragon Tail
-Earthquake/Fire Blast
-Toxic/Fire Blast
Nature: Impish
EVs: 240 HP/176 Def/92 Spe
Item: Rocky Helmet
Ability: Rough Skin
There's literally no reason to use Flygon at all, as Garchomp can do everything it does better. Tyrantrum or Goodra are better substitutes, the former for having recoil-free Head Smashes thanks to Rock Head, and the latter for having monstrous special bulk. Though they're not OU Pokemon, both have better merits over Flygon:
Tyrantrum:
-Dragon Dance
-Head Smash
-Outrage/Dragon Claw
-Earthquake/Fire Fang
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb/Lum Berry
Ability: Rock Head
or
-Head Smash
-Outrage
-Earthquake
-Superpower/Fire Fang
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Scarf/Choice Band
Ability: Rock Head
Goodra:
-Draco Meteor
-Fire Blast
-Sludge Wave/Thunderbolt
-Earthquake/Muddy Water
Nature: Modest
EVs: 240 HP/252 SAtk/16 Spe
Item: Assault Vest
Ability: Sap Sipper
