So Garchomp having 3 weaknesses and any ice move is going to kill it, we're going to want to out speed everything.
Garchomp @ Choice Scarf
Ability: Rough Skin
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Crunch
- Outrage / Dragon Claw
- Earthquake
- Aqua Tail / Iron Head / Rock Slide
Crunch: Ghost-type Coverage
Outrage / Dragon Claw: STAB
Earthquake: Do I have to explain?
Aqua Tail / Iron Head / Rock Slide: Coverage
So Earthquake needs no explanation.
If you don't want to have to deal with confusion, run Dragon Claw, if you're feeling lucky run Outrage.
Crunch is just for nice coverage against Pyschic and Ghost types.
Aqua Tail is nice coverage, with a 90 base power would do pretty good damage, Iron Head to deal with Fairies, but not recommended because some fairies might be able to take a non-STAB Iron Head to the face.
Rock Slide just for Flying types that you can't really touch with anything else unless your running Outrage, then you can touch them.
I tried it out a few times with Aqua Tail and Outrage, honestly Dragon Claw would suit me better because of how unlucky I am, but if you don't care about being confused then go for it!