Before I even rate this, I just want to say that there is no way this team crushed 90% of what you faced, and there is no way at all it won in Ubers, unless your opponents were TERRIBLE.
So. To the team itself.
Togekiss: Bad set. EVs are not the right spread for Togekiss. Togekiss's best bet is probably a Paraflinch set. Much though I HATE hax, I have no real choice but to recommend this.... Meh.
Togekiss @ Leftovers
Trait: Serene Grace
EVs: 252 HP / 4 Def / 252 SpD
- Thunder Wave
- Air Slash
The idea is to paralyze them and abuse Air Slash for flinch hax until they die. You can run Aura Sphere or Nasty Plot in place of Flamethrower but I'm recommending that here because Ferrothorn laughs at most of this team as it is. Roost is for recovery, obviously.
Liepard: This should not be used in OU. This should not EVER be used outside NU. As you have no hazard setter, I'm going to suggest the aforementioned Ferrothorn for this slot. (Anyone who knows me saw that coming xD).
Ferrothorn @ Leftovers
Trait: Iron Barbs
EVs: 252 HP / 88 Def / 168 SpD
- Power Whip
- Stealth Rock
- Leech Seed
I love this thing, and for good reason. It's probably the best hazard setter in OU, it checks a lot of threats and it can serve as an awesome physical tank in general. Power Whip gets STAB and better coverage than Gyro Ball along with reliable power. Spikes and Stealth Rock are your hazards, you should at the very least try your hardest to get Rocks up. They're amazing. Leech Seed supplements Leftovers recovery and wears the opponent down.
Porygon2 is a defensive Pokemon in OU unless you run Trick Room. You don't, so use it defensively.
Porygon2 @ Eviolite
EVs: 252 HP / 184 Def / 72 SpD
- Ice Beam
Pretty simple. Toxic is for poison, Thunderbolt and Ice Beam not only get BoltBeam coverage, but also run over Gyarados, Gliscor and Dragons like ants. Recover keeps you around. Trace over Download because you're mainly using this for defense. Trace counters Jellicent spectacularly, rendering Porygon2 immune to both its STABs and just generally walling any non-Specs Jellicent (and it's almost never used with Specs anyway) and forcing Specs to switch if timed right. It lets you wall other things too, but Jellicent is the main one.
Garchomp seems okay but put the other 4 EVs somewhere. SpD or HP recommended.
Swellow: No. Just no. It will die. Before killing anything, if your opponent is smart. You also have no Fire presence on your team so I'll recommend a Heatran here.
Heatran @ Air Balloon
Trait: Flash Fire
EVs: 252 SpA / 4 SpD / 252 Spe
- Fire Blast
- Earth Power
- Hidden Power Grass/Ice
- Flame Charge
You start with Flame Charge to boost your Spe stat to sweeping levels and start attacking. Fire Blast is your main move especially if you got a Flash Fire boost. Speaking of Flash Fire, it's great for taking Fire moves aimed at your Ferrothorn. Anyway, Earth Power hits opposing Fire-types, especially Heatrans unless they have an Air Balloon active. You can really use either Grass or Ice, but I recommend Grass since it gives you an answer to Gastrodon that isn't Ferrothorn. The reason? Ferrothorn doesn't appreciate Earthquake. Heatran doesn't care so long as it has its Balloon, and it outspeeds with enough power for an OHKO (Pretty sure anyway, computer can't run the calcs to confirm for some reason)
Finally, this is a pretty standard Cloyster, but change the EV spread to 252 Atk / 4 SpA / 252 Spe. Defensive investments don't mean squat if you use Shell Smash. I don't really like Cloyster though, mainly because Priority destroys it....
"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