If yu listin here then i suppose you need to give roles while creating team two ghost types doesn't really fit together as well you only have 1 attacker and 1 sp.attacker and the rest of the team is wall your team (expect hippodown and garchomp) can easily be taken down by a alolen muk! As I see you can take gastrodon insted jellicent and or rotom wash.
Next hippodown and garchomp since you already have clef and skarmory you might replace hippodown with any sweeper and if you are making a mega garchomp team then replace clef or skarmory instead of hippodown to a sweeper since mega garchomp has sand force ability you can take tyrantar or hippodown but then you might as well switch to a sand team.
Here's a sand team for getting you started!
Hippowdown @ smooth rock
Ability: Sand stearm
Evs: Def-252 Sp def- 4 Hp-252
Nature- impish
Slack off
Earthquake
Super power
Sleath rock
Tyraintar @ idk
Nature- idk
Ability- sand stearm
Dragon dance or slealth rock
Earthquake
Fire punch
Stone edge
Mega garchomp @ garchompite
Ability- sand force
Nature- jolly
Sword dance
Earth quake
Posion jab/ fire fang
Dragon claw
Stoutland @ choice band
Nature jolly
Ability- sand rush
Thunder fang
Super power
Play rough
Stomping tantrum
Excadrill @ choice band/ choice scarf/life orb(if you chose life orb the ability should be sand rush)
Ability- sand rush/sand force
Nature jolly
Earth quake
Iron head
Rapid spin(you will have to instantly switch also since it will be banded or scarfed/life orb will hold a different story)
4th attack decide on your own!
Landrus @ choice Scarf
Ability- sand force
Nature-naive
Earthquake
Super power
Stone edge
H.p ice or whatever you like
My honest opinion I would not recommend garchomp since it is greatly outclassed by all othe mega due to its speed stat you can replace garchomp by gastrodon if you need a special defender for your team and take tyraintar for mega if you are taking mega tyraintar then take dragon dance or whatever next is landrus is you don't own it yet then
You can take rotom(any form) or glisicor for a defoger role or fill that spot by any pokemon you want and finally about the ""idk"" part on tyraintar its if you chose mega tyraintar then item will be tyraintarite amd ability should be jolly or if you still chose mega garchomp then i really don't know the item or nature
Hope it helps(As I don't really know if you might get what i said xd)