This is my thinking for a competitive team. Any changes?

[Noctis]

So the team im thinking of is:
Gengar(gengarite):
nature: Modest
moveset: Hypnosis
Dream Eater
Toxic
Shadow Ball

Garchomp(Rockium Z):
nature: Rash
moveset: Rock Slide
Crunch
Earthquake
Dragon Claw

Toxapex(Black Sludge):
nature: Rash
moveset: Toxic
Venoshock
Liquidation
Protect

Tapu Koko(Tapunium Z):
nature: Rash
moveset: Nature's Madness
Thunderbolt
Calm Mind
Taunt

Skarmory(Leftovers):
nature: Quiet
moveset: Autotomize
Brave Bird
Roost
Iron Head

Conkeldurr(Black Belt):
nature: Adamant
moveset: Bulk Up
Stone Edge
Hammer Arm
Drain Punch

Anything i could change? Let me know. I'm open to any ideas.

 

[Nah]

gonna need to fill in EVs and abilities too if you're looking to battle other people with this

Some of the natures could use to be changed too, if you can. Rash and Quiet aren't really the natures any of the Pokemon who have them want. Skarm wants something to boost Defense/Sp.Def and reduce Sp.Atk (so Impish or Careful), while Koko wants Timid to boost its impressive Speed further. Physical attacker Garchomps like Jolly.

Toxapex is also built to be a defensive 'mon, so you'll need to squeeze Recover in there somewhere. Baneful Bunker can be used over Protect, if you want, as it does the same thing but comes with the added bonus of poisoning opponents that use a move that makes contact with it.

probably also gonna want to get Stealth Rock the team too

 

[gimmepie]

Is this for VGV or smogon?
Also don't forget items!

 

[Kurapika]

Gengar
Generally, people switch away their Pokémon after you put it to sleep. Mega Gengar's ability prevents that so that's an interesting play with Hypnosis, the low accuracy tho is a gamble game... Toxic is of no use for Gengar imo, except in a scenario where you will switch out to Toxapex/Skarmory I guess.
Garchomp
Z-moves are meant to One-Shot and you are losing STAB damage with Rock type Continental Crash, but it is still an interesting approach to surprise certain Flying/Ice/Bug targets when they wouldn't expect it. Stealth Rock can be good here as a remplacement to Crunch, following Nah's suggestion.
Toxapex
Venoshock sounds not very interesting with Toxic imo. You should probably go Baneful Bunker/Venoshock/Recover/Liquidation or Toxic/Recover/Liquidation/(Insert another move like Knock Off, Haze, Sludge Bomb, ...).
Tapu Koko
The moveset of your Tapu Koko sounds kinda bad to me, combining Calm Mind and Nature's Madness... Maybe you can replace Nature's Madness with Hidden Power (Ice) or Dazzling Gleam and even take Roost instead of Taunt? Roost and Calm Mind can be a good mix.
Skarmory
Autotomize and Iron Head are kind of unusual on Skarmory, could've been interesting if it had Serene Grace. the classic Spikes/Whirlwind are probably more interesting for you.
Conkeldurr
I understand you want to deal the maximum damage here, but Black Belt is kind of meh tbh, Hammer Arm is such an unappealing move too. You are better off considering Leftovers as well as Ice Punch and Knock-Off/Mach Punch instead of Stone Edge and Hammer Arm. Ice Punch, with Iron Fist, deals almost the same damage as Stone Edge, and has 100% accuracy.

 

[DragonKing48]

Garchomp only has Ice and Fairy weakness besides Dragon. Iron Head takes care of both instead of Crunch.