Hippowdon - I like to run Toxic > Whirlwind but that is just my preference. therwise it looks great.
Landorus - Instead of Sand Force run Sheer Force, and change his item from Yache Berry to Life Orb. next you will want to replace HP Fire for HP Ice, as Dragon and Flying types wall you, and Focus Blast will take care of Ice types.
Stoutland - I LOVE Stoutland, and I see what you are doing with this set, but I am going to suggest you a set that just plows through anything that isn't a Ghost or Steel type, and even some Steel types can't take his Return at low HP.
Stoutland @ Choice Band
Trait: Sand Rush
EVs: 4 HP / 252 Atk / 252 Spd
This Stoutland does 2 things, trap and sweep. Crunch and Pursuit are great for eliminating Gost and Psychic types that may give you trouble, Superower covers Steel and Rock types, and Return just destroys stuff, and with a Choice Band his attack is pretty high. Adamant can be run for maximum power, but if your run Adamant you are outsped (Even in the sand) by Choice Scarf Terrakion, so you may want to run Jolly if Terrakion starts to give you toruble.
Camerupt - No offense but Camerut sucks. Not your set, just Camerupt in general. In place of Camerupt I am going to suggest to you something that will work wonder with Stoutland. Gengar. Gengar can use his great sweeping stats to weed out the Ghost and Steel types that give Stoutland trouble.
Gengar @ Life Orb
EVs: 4 HP / 252 SAtk / 252 Spd
- Shadow Ball
- Focus Blast
- Hidden Power [Ice]/Thunderbolt
- Pain Split
Ferrothorn - Ferrothorn look pretty good, but I'll be changing the EVs, and 1 move. Change the EVs to 252 HP / 72 Def / 180 SDef, and change Giga Drain to Power Whip.
Garchomp - Chomp is good, but I am going to replace im for 2 reasons.
- Dat Ice
- Garchomp is extrmeley standard and we need something to set this team apart.
So in place of Chompy, I suggest Vaporeon, as it can suck up Water attacks and Ice attacks that plage your team, giving him lots of chances to set up Wish, healing damaged allies.
Vaporeon @ Leftovers
Trait: Water Absorb
EVs: 252 HP / 248 Def / 8 Spd
- Roar/Ice Beam/Toxic