This team is OU I'm guessing? If that's the case then Gastrodon over Swampert
Gastrodon @ Leftovers
Trait: Storm Drain
EVs: 252 HP / 4 SpA / 252 SpD
Pretty standard wall set here. You liked EQ and Scald on Swampert, so I stuck both on Gastrodon. Toxic for status damage, which is always great. Recover should be pretty self-explanatory, healing off damage alongside Leftovers. Storm Drain gives you a Water immunity (yes, IMMUNITY) and +1 SpA if you take a Water move. You can opt to run Earth Power over Earthquake to capitalize more on that, and if you choose to do so you could run Calm over Sassy, as the Atk drop would be meaningless then.
Arcanine is another UU Pokemon with a better replacement in OU - Infernape. Infernape can run a very dangerous mixed attacking set, or you can go purely one way or the other. I'll give a mixed set here, as it is my favorite by far:
Infernape @ Life Orb
Trait: Iron Fist
EVs: 252 Atk / 4 SpA / 252 Spe
- Close Combat
- Mach Punch
This is the set I prefer with Infernape, although you can run Grass Knot and Stone Edge (among many others - Infernape has 4-move syndrome BAD). Overheat is your Special attack, and it's really a one-off thing. This is the reason for using Iron Fist - Blaze will rarely trigger. Iron Fist affects both Close Combat and Mach Punch, although it doesn't boost them much it does so all the time and capitalizes on the more dangerous Physical aspect of the set. Close Combat is your main STAB move, and the move you'll use most of the time. I really like U-Turn - it gives you a bit of damage and the always-useful switch advantage if they bring in a counter on the same turn. Mach Punch is for priority, which can be amazingly useful for revenge killing.
On Hydreigon, Fire Blast over Flamethrower. The extra power is very noticeable and 85% accuracy is perfectly fine. You could also change Focus Miss to Surf if the accuracy becomes an issue, especially as Fire Blast deals with Ice and Steel Pokemon that would be handled by it.
Thundurus looks solid, although I'm not familiar with it at all.
Gallade is not great in OU. I'd replace it too. If you want another physical attacker, you might try something like Breloom.
Breloom @ Life Orb
EVs: 4 HP / 252 Atk / 252 Spe
- Mach Punch
- Bullet Seed
Another set I like a lot, although I usually use Ferrothorn as my Grass-type. I haven't even gotten around to trying Amoonguss, I use Ferro so much. Anyway, Spore is obvious awesome 100% Sleep. Mach Punch gets a Technician boost and priority, which combines to be really nice. Bullet Seed also gets a Technician boost, and can be potentially devastating. It's unreliable as you may hit only twice, but it's still your main attack. I like Sub even on this set for a few reasons. First, it protects you from Burns since you don't have a Toxic Orb to do that. Second, it takes hits for you, which is always nice. The main reason here is to block statuses that ruin your fun though.
Finally, Skarmory seems good but I'd go for Leftovers over Shed Shell since trappers are pretty rare (for me anyway, I never see them. Thankfully. I'm using Mono-Steel at the moment, Magnezone murders it xD).
"Whether Castform the Weather Pokemon can weather the weather is dependent on whether the weather that it's weathering is the proper weather for it to weather. Whether the opponent can weather the weather is also subject to whether the weather that it's weathering is the right weather to weather. Whether Castform can weather the opponent is once again dictated by the weather and whether that weather is the favorable weather for weathering. But most importantly, you should know whether there will be weather to weather rather than what weather they will be weathering and whether they can weather that weather."
- Smogon's Castform analysis