Newbie LF help finishing VGC Team

[Apo]

Hey guys :P

I want to start competitive battles, but mostly for fun, do not really plan to go to any event but I need help

Did not play Pokemon for years, so all of this is a mix of what I want to play, infos from the internet and my own thoughts since i like the strategy aspect

Mega Venusaur Venusaurite Thick Fat

Sludge Bomb
Giga Drain
Leech Seed
Protect

Gengar Focus Sash Levitate

Sludge Bomb
Icy Wind
Will-O-Wisp
Taunt

Garchomp Life Orb Rough Skin

Rock Slide
Earthquake
Dragon Claw
Protect

Clefable Sitrus berry Magic Guard

Follow Me
Heal Pulse
Moonblast
Protect

I always liked Venusaur, because Bulbasaur was the hated one :S lol and his bulk+regen is nice in Mega. Garchomp felt necessary for the Rock Slide to cover the Flying weakness. Also Eartquake can be used with Gengar's Levitate. Fairy types would be covered by Mega Venusaur Sludge Bomb.
I am stuck on those 4. Seems like this Gengar would outspeed an Adamant Mega Salamence and has 43.8% to OHKO it with Icy Wind, and Clefable would OHKO for sure but won't outspeed it. Mega Kangaskhan should not be a problem since it cannot go through Mega Venusaur bulk + Giga Drain.

I feel like I need some Fighting, and/or something to counter Fire types
I was thinking about Arcanine with Close Combat to make sure to OHKO Mega Kangaskhan and the Intimidate could be usefull, maybe a Tailwind user like Suicune?

I am a Newbie, so I will take all the advices