Your team needs a complete makeover.
Roserade: If you want a defensive grass type, go Ferrothorn or Tangrowth. If you want an offensive one, Serperior is by far the best option. Roserade is too slow and too frail.

Ferrothorn @ Leftovers / Rocky Helmet
Ability: Iron Barbs
EVs: 252 HP / 60 Def / 196 SpD
Sassy Nature
- Gyro Ball
- Spikes
- Stealth Rock / Leech Seed
- Protect / Power Whip

Tangrowth @ Rocky Helmet
Ability: Regenerator
EVs: 252 HP / 252 Def / 4 SpD
Relaxed Nature
- Sleep Powder
- Knock Off
- Giga Drain
- Hidden Power [Ice] / Sludge Bomb
Tangrowth @ Assault Vest
Ability: Regenerator
EVs: 252 HP / 8 Def / 248 SpD
Sassy Nature
- Giga Drain
- Knock Off
- Sludge Bomb
- Hidden Power [Ice] / Earthquake

Serperior @ Leftovers
Ability: Contrary
EVs: 248 HP / 8 SpA / 252 Spe
Timid Nature
- Leaf Storm
- Hidden Power [Fire]
- Substitute
- Leech Seed / Glare
Gallade: It isn't actually bad in OU. You can use other Fighting types like Mega Medicham, and Special Psychics like Mega Alakazam and Tapu Lele, but it is still a pretty decent Pokemon. I'd suggest adjusting your set, however.

Gallade-Mega @ Galladite
Ability: Justified --> Inner Focus
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Close Combat
- Zen Headbutt
- Knock Off
- Swords Dance / Ice Punch
Staraptor: There are so many better Flying types in OU, which have better defensive or offensive use.

Landorus-Therian @ Flyinium Z
Ability: Intimidate
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Earthquake
- Fly
- Swords Dance
- Stealth Rock

Tornadus-Therian @ Fightinium Z
Ability: Regenerator
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Hurricane
- Knock Off
- Defog
- Focus Blast
Empoleon: There are better Water and Steel types with more Speed or offensive power. Empoleon is too slow and weak.

Magearna @ Assault Vest
Ability: Soul-Heart
EVs: 248 HP / 24 Def / 200 SpD / 36 Spe
Calm Nature
- Fleur Cannon
- Volt Switch
- Ice Beam
- Hidden Power [Fire]
Magearna @ Choice Specs
Ability: Soul-Heart
EVs: 4 Def / 252 SpA / 252 Spe
Timid / Modest Nature
- Fleur Cannon
- Volt Switch
- Ice Beam
- Focus Blast / Aura Sphere

Heatran @ Leftovers
Ability: Flash Fire
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
- Magma Storm
- Taunt
- Stealth Rock
- Earth Power

Greninja @ Life Orb
Ability: Protean
EVs: 4 Atk / 252 SpA / 252 Spe
Hasty / Naive Nature
- Ice Beam
- Gunk Shot
- Hidden Power [Fire]
- Hydro Pump

Greninja-Ash @ Choice Specs
Ability: Battle Bond
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Hydro Pump
- Dark Pulse
- Ice Beam
- Spikes / Grass Knot
Or use Ferrothorn
Mamoswine: Bad defensive typing, too slow. I've said this before and I'll say this again, there are better options
You can use the Landorus-Therian set I provided above

Garchomp @ Life Orb
Ability: Rough Skin
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Outrage / Dragon Claw
- Earthquake
- Fire Fang
- Swords Dance / Stealth Rock

Gliscor @ Toxic Orb
Ability: Poison Heal
EVs: 244 HP / 8 Atk / 12 SpD / 244 Spe
Jolly Nature
- Earthquake
- Facade
- Swords Dance
- Stealth Rock / Protect / Roost / Substitute / Toxic

Weavile @ Choice Band
Ability: Pickpocket
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Icicle Crash
- Knock Off
- Ice Shard
- Pursuit
Rotom-Heat: You generally don't want your pivot to be weak to Stealth Rock. Rotom-Wash can deal with Ground types trying to block Volt Switch, and is not weak to Stealth Rock

Rotom-Wash @ Leftovers
Ability: Levitate
EVs: 252 HP / 150 Def / 50 SpD / 56 Spe
Bold / Timid Nature
- Hydro Pump
- Volt Switch
- Will-O-Wisp
- Defog / Pain Split