Looking to build my first competitive team, need some help!

[Dugfire180]

I hope this is a good place to post this! Let me know if it needs moved or anything of the sort!

So I've been playing since gen1, but I've never gotten into the competitive scene, I'm looking to change that this generation. So far I have 5 out of 6 pokemon picked out for my team and I'm really struggling to pick a sixth, I've been bouncing around some ideas but I still need some help.

Here is my team so far:

Glimmora @ Rocky Helmet
Ability: Toxic Debris
Level: 50
Tera Type: Grass
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Spiky Shield
- Stealth Rock
- Mortal Spin
- Earth Power

Meowscarada @ Life Orb
Ability: Protean
Level: 50
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Flower Trick
- Knock Off
- Thunder Punch
- U-turn

Cetitan @ Assault Vest
Ability: Thick Fat
Level: 50
Tera Type: Steel
EVs: 252 HP / 252 Atk / 4 SpD
Adamant Nature
- Earthquake
- Ice Shard
- Ice Spinner
- Heavy Slam

Volcarona @ Heavy-Duty Boots
Ability: Flame Body
Level: 50
Tera Type: Water
EVs: 4 HP / 252 SpA / 252 Spe
Modest Nature
- Quiver Dance
- Fiery Dance
- Bug Buzz
- Giga Drain

Dragapult @ Choice Band
Ability: Clear Body
Level: 50
Tera Type: Dragon
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Dragon Darts
- U-turn
- Sucker Punch
- Phantom Force

So for my last guy I've been toying around with the idea of either Slowking to set up snow for the Cetitan, or Magnezone for some extra coverage. Other than that I'm kinda of lost of who to choose or what would be a good fit for my team.
Any help would be amazing, be it who would be a good sixth, or if the builds on my current mons aren't that great.

 

[Dusk Mage Necrozma]

Go to the Rate My Team subforum. Note that you have to give 3 lines of description for each team member choice.