[RATE MY TEAM] Need help for my team

[RPS_MCH72]

Hi
I'm new to competitive battling, this is actually my first attempt at building a team. Obviously I know there's gonna be a lot of problem with the team and I hope someone can help me make it better

I don't really know what I'm trying to do with this team or what my strategy is, I just got a shiny Sableye which is my favorite pokemon and wanted to make a team base around Mega Sableye. Just fyi it doesn't have recover and has prankster when not mega evolved. If recover is absolutely needed I have a non shiny one I could put in but I just put this one in for now because I want to make it work lol.

Also I don't really understand how to give pokemon a desired HP so I try to avoid them :P.

So with that being said, here is the team :
Sableye-Mega @ Sablenite
Ability: Magic Bounce
Shiny: Yes
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Confuse Ray
- Power Gem
- Foul Play
- Shadow Ball

Dragalge @ Assault Vest
Ability: Adaptability
EVs: 248 HP / 252 SpA / 8 SpD
Modest Nature
- Draco Meteor
- Sludge Wave
- Scald
- Icy Wind

Gardevoir @ Choice Scarf
Ability: Trace
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Moonblast
- Psyshock
- Focus Blast
- Shadow Ball

Skarmory @ Rocky Helmet
Ability: Sturdy
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Roost
- Whirlwind
- Stealth Rock
- Brave Bird

Diggersby @ Choice Scarf
Ability: Huge Power
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Return
- Earthquake
- Wild Charge
- U-turn

Slowbro @ Leftovers
Ability: Regenerator
EVs: 252 HP / 252 Def / 4 SpA
Bold Nature
- Calm Mind
- Scald
- Psyshock
- Slack Off

Thanks to everyone for your help