Stuck on the Ladder

[toasterwaffles]

This is my second effort at making a competitive team, and I'm stuck around 1200 on the Showdown ladder (Gen 7 pokebank OU). Is there any way to make this team viable, or should I just scrap it and try something new? Any sort of suggestions would be helpful.

Toxapex @ Black Sludge
Ability: Regenerator
EVs: 248 HP / 252 Def / 8 SpD
Bold Nature
IVs: 0 Atk
- Scald
- Toxic Spikes
- Haze
- Recover

Mudsdale @ Rocky Helmet
Ability: Stamina
EVs: 248 HP / 252 SpD / 8 Spe
Careful Nature
- Rest
- Earthquake
- Heavy Slam
- Toxic

Clefable @ Leftovers
Ability: Magic Guard
EVs: 248 HP / 8 Def / 252 SpD
Calm Nature
IVs: 0 Atk
- Aromatherapy
- Wish
- Stealth Rock
- Moonblast

Salazzle @ Black Sludge
Ability: Corrosion
EVs: 248 HP / 8 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Substitute
- Disable
- Toxic
- Flamethrower

Decidueye @ Decidium Z
Ability: Overgrow
EVs: 248 HP / 252 Atk / 8 SpD
Adamant Nature
- Spirit Shackle
- Swords Dance
- Defog
- Leaf Blade

Gyarados-Mega @ Gyaradosite
Ability: Mold Breaker
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Waterfall
- Crunch
- Earthquake
- Dragon Dance

I'm trying not to use pokemon that are not obtainable in sun/moon because I'd ultimately like to use this team on the in-game ladder and I don't have access to pokebank, but I'm testing it in pokebank OU because I want it to be able to take on any pokemon team. Thanks for helping me out.

 

[PlatinumDude]

Replace Mudsdale with Gastrodon or Zygarde, as the former has reliable recovery and the latter has Thousand Arrows to nail fliers, along with a priority move in Extreme Speed to hit faster attackers with:

Gastrodon:
-Curse
-Scald
-Earthquake
-Recover
Nature: Sassy
EVs: 252 HP/112 Def/144 SDef
Item: Leftovers
Ability: Storm Drain

or
-Scald
-Earthquake/Ice Beam
-Toxic
-Recover
Nature: Relaxed/Bold
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
Ability: Storm Drain

Zygarde:
-Substitute
-Coil
-Thousand Arrows
-Extreme Speed/Toxic
Nature: Careful
EVs: 240 HP/212 SDef/56 Spe
Item: Leftovers
Ability: Aura Break

or
-Dragon Dance
-Outrage
-Thousand Arrows
-Extreme Speed
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb/Lum Berry
Ability: Aura Break

I'm questioning Salazzle's usefulness on this team because it's straight-up walled by Heatran. The only thing it can do against it is Toxic before switching out. Marowak pairs well with Toxapex; it can take its Electric attacks thanks to Lightning Rod and can hit Heatran hard on the switch with Bonemerang:
-Flare Blitz/Fire Punch
-Shadow Bone
-Bonemerang/Stealth Rock
-Will-o-Wisp/Stealth Rock
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Thick Club
Ability: Lightning Rod