Although I'm not allowed to post another set, I do feel that Golurk is an admirable counter to both Zapdos and Terrakion.
With the smogon OU set(
http://www.smogon.com/bw/pokemon/golurk/ou) and taking calculations, 0 SpA Zapdos Hidden Power Ice vs. 252 HP / 0 SpD Golurk: 146-174 (38.21 - 45.54%) -- guaranteed 3HKO
Terrakion has no good option vs Golurk:
252 Atk Choice Band Terrakion Stone Edge vs. 252 HP / 176+ Def Golurk: 109-129 (28.53 - 33.76%) -- possible 4HKO
In sharp contrast, Golurk has good options against both of these pokemon:
80 Atk Golurk Earthquake vs. 4 HP / 0 Def Terrakion: 306-360 (94.44 - 111.11%) -- 68.75% chance to OHKO
80 Atk Iron Fist Golurk Ice Punch vs. 252 HP / 0 Def Zapdos: 192-226 (50 - 58.85%) -- 72.66% chance to 2HKO
This essentially means that Golurk can switch in on a Thunderbolt/Close Combat, set up SR and wreak havoc.
I think Golurk is a viable solution because Terrakion can do NOTHING against it and after a CC Golurk can switch in and sweep.
If Terra goes for Stone Edge after a defense decrease(via CC before Golurk switched in), 80 Atk Golurk Earthquake vs. -1 4 HP / 0 Def Terrakion: 456-536 (140.74 - 165.43%) -- guaranteed OHKO
This is why I claim Golurk is best: it has ready answers for both Zapdos and Terrakion, can freely switch in on Volt Switch, CC or Quick Attack and can prevent Zapdos from Roosting(EQ OHKOes if zapdos roosts)
As I see a lot of people have put up multiple sets but only one for voting, I have decided to put up my set for voting(not Whimsicott)
Golurk @ Leftovers
Trait: Iron Fist
EVs: 80 Atk / 252 HP / 176 Def
Impish Nature
- Earthquake
- Ice Punch
- Shadow Punch
- Stealth Rock
As I stated above earlier, Golurk is a good counter for Stone Edge(not taking much damage from the attack) and can OHKO with Earthquake(if it comes in after a Close Combat then guaranteed OHKO)) as well as a good counter for Zapdos. It also allows us to set up Stealth Rock, deterring pokemon like Weavile from being chosen for team 1. Shadow Punch deters pokemon like Alakazam and takes care of psychic types in general as well as ghost types. Ice Punch is a deterrent to pokemon like Garchomp and Dragonite(to name a few) and E-Quake takes care of any Rock pokemon like Terrakion.
The disadvantages of this set? Weakesses to Dark, Water and Grass mean that it will need a Steel type to form a defensive Core, although Slowbro can take Water-types all day long. Maybe Bisharp might form a good core with Golurk, resisting Dark and Grass and Golurk covering the fighting and ground.
Also, I would like to comment on some of the sets that have been proposed.
Firstly, Gastrodon, Swampert and Seismitoad while good sets cannot handle a grass-type or even a surprise HP-grass on any decent pokemon. Volcarona Giga Drain can ohko all three. More importantly, Swampert(the best set out of the three Water/Ground) is REALLY slow and thus cannot outspeed HP grass on most.
Garchomp is a big no simply because of Weavile: Weavile Ice Shard OHKOes Garchomp. On the other hand, this is the damage it does to Golurk: Ice Shard: 38.74 - 45.54%(3HKO). Essentially even if Weavile switches in to Golurk, Golurk has enough bulk to take a hit and STAB back with E-Quake. More importantly though, Golurk has SR to dissuade Team 2 from picking Weavile.
Jirachi is definitely a good idea because of the Paraflinching. The only issue with Jirachi is that, as alexwolf himself mentioned, being a defensive pokemon limits Team 1's offensive capabilities.
Jirachi does make the team even more weak to Volcarona though(Giga Drain for Slowbro, Fiery Dance for Jirachi). What's worse, Fiery Dance has chances to boost SpA so Jirachi can't keep Wishstalling because after a single boost: +1 252 SpA Life Orb Volcarona Fiery Dance vs. 252 HP / 152+ SpD Jirachi: 413-486 (102.22 - 120.29%) -- guaranteed OHKO
Hell, after a Quiver Dance, Fiery Dance is OHKO so even if Jirachi switches in on a quiver dance, game over.
Golurk on the other hand can OHKO with Earthquake.
Conkeldurr appeals to me because of the ability to take a hit like Jirachi and is also not Volcarona weak.
I hope to see further discussion. As of now, I am withdrawing Whimsicott and nominating my Golurk set.