I don't think Mawile has time for Pain Split. Mawile is also strong enough that it doesn't need Foul Play (though it does see use in the RestTalk set to compensate for the lack of Attack EVs in that set). It's also slow, so it needs Sucker Punch to make up for its bad Speed:
-Play Rough
-Sucker Punch
-Fire Fang/Iron Head/Swords Dance
-Swords Dance/Substitute
Nature: Adamant
EVs: 132 HP/252 Atk/124 Spe
Item: Mawilite
Ability: Intimidate
or
-Rest
-Sleep Talk
-Play Rough
-Foul Play
Nature: Impish
EVs: 248 HP/252 Def/8 SDef
Item: Mawilite
Ability: Intimidate
Offensive Dragon Dance Gyarados uses Life Orb or Lum Berry as the item. The former gives Gyarados better damage output, while the latter lets Gyarados shrug off a status once.
Salamence has fallen out of favor in the OU environment because of its inability to deal with Fairies apart from the inaccurate Iron Tail. Half of your team is currently weak to Stealth Rock and that's a bad thing. Other Dragon Pokemon to consider are Goodra and Garchomp:
Goodra:
-Draco Meteor
-Fire Blast
-Thunderbolt/Earthquake
-Dragon Tail/Earthquake
Nature: Quiet/Sassy
EVs: 248 HP/252 SAtk/8 SDef
Item: Assault Vest
Ability: Gooey/Sap Sipper
or
-Draco Meteor
-Fire Blast
-Thunderbolt
-Focus Blast
Nature: Modest
EVs: 248 HP/252 SAtk/8 SDef
Item: Choice Specs
Ability: Gooey/Sap Sipper
or
-Dragon Pulse
-Flamethrower
-Thunderbolt
-Toxic/Dragon Tail
Nature: Calm/Sassy
EVs: 248 HP/8 Def/252 SDef
Item: Leftovers
Ability: Gooey/Sap Sipper
Garchomp:
-Swords Dance
-Outrage/Dragon Claw
-Earthquake
-Fire Fang/Stone Edge
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Lum Berry/Yache Berry
or
-Outrage
-Earthquake
-Fire Fang/Aqua Tail/Stone Edge/Fire Blast
-Dragon Claw/Dual Chop
Nature: Jolly/Naive
EVs: 4 HP/252 Atk/252 Spe
Item: Choice Band/Choice Scarf
or
-Stealth Rock
-Outrage/Dragon Claw
-Earthquake
-Fire Blast/Toxic
Nature: Impish
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers/Rocky Helmet
Ability: Rough Skin
Mandibuzz is one of the best Defoggers out there. If I were you, I'd take advantage of that fact. Lax is also a terrible nature to use competitively, as it wastes away Mandibuzz's good Special Defense. Take note that Foul Play doesn't use Mandibuzz's Attack; it uses the opponent's Attack to calculate damage:
-Foul Play
-Roost
-Defog
-Toxic/Whirlwind/Knock Off
Nature: Bold/Impish
EVs: 248 HP/252 Def/8 SDef
Item: Leftovers
Ability: Overcoat
Forretress is rather subpar now. The better hazard setters to use are Ferrothorn and Skarmory:
Ferrothorn:
-Spikes/Stealth Rock
-Leech Seed
-Gyro Ball/Thunder Wave
-Power Whip/Protect
Nature: Relaxed
EVs: 252 HP/48 Def/208 SDef
Item: Leftovers
Ability: Iron Barbs
Skarmory:
-Roost
-Whirlwind
-Stealth Rock/Spikes/Brave Bird
-Defog/Brave Bird
Nature: Bold/Impish
EVs: 252 HP/252 Def/4 SDef or 252 HP/16 Def/240 SDef
Item: Leftovers/Rocky Helmet
Ability: Sturdy
or
-Spikes
-Roost
-Whirlwind
-Taunt/Brave Bird
Nature: Bold/Impish
EVs: 252 HP/184 Def/72 Spe
Item: Leftovers/Rocky Helmet
Ability: Sturdy