Here's my current team choices and strategies. You all will notice I have three Madeleines. That's because I can't decide which one to choose, but I'm leaning towards the Houndour or the Cleffa:
Snover (Petit Four)
Weak: Fighting Flying Poison Rock Bug Steel Fire
Resist: Ground Water Grass Electric
Strong-Stat: Balanced -Speed
Item: Oran Berry
EVs: 116 HP 180 Attack 180 SpA
Nature: Lonely
Moves
Protect
Blizzard [Ice]
Ice Shard [Priority Ice]
Energy Ball [Grass]
Spheal (Éclair)
Weak: Fighting Rock Grass Electric
Resist: Water Ice
Strong-Stat: HP/Def/SpD -Speed
Ability: Ice Body
Item: Leftovers
EVs: 196 HP 196 Defense 76 Speed 36 SpD
Nature: Timid
Moves
Protect
Substitute
Toxic
Surf [Water]
Staryu (Nonpareils)
Weak: Grass Electric
Resist: Steel Fire Water Ice
Strong-Stat: Speed/SpA -HP
Ability: Natural Cure
Item: Life Orb
EVs: 76 Defense 236 Speed 196 SpA
Nature: Modest
Moves
Hydro Pump [Water]
Thunderbolt [Electric]
Blizzard [Ice]
Hidden Power [Ground]
Bronzor (Biscuit)
Weak: Ground Fire
Resist: Normal Flying Rock Steel Grass Psychic Ice Dragon
Immune: Poison [Ground with Levitate Ability]
Strong-Stat: HP/Def/SpD -Speed
Ability: Levitate
Item: Oran Berry
EVs: 140 HP 4 Attack 228 Defense 12 Speed 4 SpA 68 SpD
Nature: Adamant
Moves
Stealth Rock
Gyro Ball [Steel]
Earthquake [Ground]
Light Screen
Tentacool (Fondant)
Weak: Ground Electric Psychic
Resist: Fighting Poison Bug Steel Fire Water Ice
Strong-Stat: SpD/Speed -Defense
Ability: Clear Body
Item: Oran Berry
EVs: 196 Speed 116 SpA 196 SpD
Nature: Hasty
Moves
Protect
Toxic Spikes
Rapid Spin [Normal]
Blizzard [Ice]
Cleffa (Madeleine)
Weak: Fighting
Immune: Ghost
Strong-Stat: HP/SpD -Speed
Ability: Magic Guard
Item: Focus Sash
EVs: 236 Speed
Nature: Hasty
Moves
Endeavor [Normal]
Protect
Encore
Thunder Wave
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Houndour (Madeleine)
Weak: Fighting Ground Rock Water
Resist: Ghost Steel Fire Grass Ice Dark
Immune: Psychic
Strong-Stat: SpA/Speed -HP
Ability: Flash Fire
Item: Life Orb
EVs: 196 Attack 76 Speed 196 SpA 36 SpD
Nature: Lonely
Moves
Sucker Punch [Priority Dark]
Fire Blast [Fire]
Crunch [Dark]
Substitute
Diglett (Madeleine)
Weak: Water Grass Ice
Resist: Poison Rock
Immune: Electric
Strong-Stat: Speed/Attack -HP
Ability: Arena Trap
Item: Choice Scarf
EVs: 36 HP 236 Attack 236 Speed
Nature: Hasty
Moves
Earthquake [Ground]
Sucker Punch [Priority Dark]
Hidden Power [Ice]
Pursuit [Dark]
Snover is my lead, or, in this case, my Anti-Lead. He'll induce a permanent (until changed) Hail effect on the battlefield which will damage 1/16 of Max HP of non-Ice Pokémon, increase Blizzard's effectiveness to 100%, and give Spheal an extra 1/16 of healing thanks to Spheal's ability. From there Snover will Protect to block whatever move the other trainer's lead will use. Turn ends, and Hail will deal damage to break the other Pokémon's chance of using Focus Sash unless it recovers. Snover will then switch out to something that can resist the lead, or actually attack with one of its attacks if it can score a kill. Most of the Pokémon choices listed are Pokémon Snover can switch into reliably.
The most obvious move to predict is the opponent will either switch its lead to a Fire type, or the lead itself will use a Fire type — and hopefully you'll see a Fire type move being used when Snover Protects itself. From there, the most appropriate actions in order of best-to-use will be to switch to Houndour to absorb the Fire attack and sweep, switch to Tentacool to sponge a Fire attack and set up Toxic Spikes, or switch Cleffa into an attack — if you can guarantee an attack that will reduce Cleffa to 1 HP — and use Endeavor.
When Houndour fights a Pokémon that resists its attacks (it's hard to resist Fire or Dark), when Tentacool has set up Toxic Spikes and can't do attacks, or when Cleffa Endeavors and (most probably) dies along with the other current Pokémon, switch into Bronzor for defense, set up Stealth Rock, then damage with Gyro Ball for Same-Type Attack Boost damage or Earthquake. The obvious Bronzor counter is, again, a Fire type. Best choice of action is to either switch into Houndour again, or try your hand at Staryu or Spheal. Diglett is also an option to bring in if one of your Pokémon die.
Staryu and Spheal will take a bit more prediction, and are best used when they can safely come into an attack. Staryu can easily come in on a Pokémon that can't damage it super effectively, and more-easily come in on a Pokémon that only has moves it's resistant against. From there it can sweep with its multiple attack types. Spheal just needs to come in safely, Protect itself to heal in Hail, then survive to use a Substitute. After using Substitute, keep using Protect and Surf, and cast Substitute when necessary. The healing from Leftovers and Hail together should be able to keep teams stalled enough for the other traps to do their work.
If Diglett is used on the team, Diglett can be used to Revenge Kill, or to sponge any Electric-type attacks, which this team will be receiving. Snover can fulfill the Electric-type sponging role if Diglett isn't in the team.
If any traps are used against you, bring in Tentacool. Tentacool will absorb Toxic Spikes and can Rapid Spin away other arena traps.
Well? People's thoughts? Tear it apart and see if there's something obvious I'm overlooking. I know I'm strapped for attacks that can do Super-Effective damage, but a lot of my attacks can hit for neutral damage — especially Blizzard. Also, out of all the Madeleine choices — Houndour, Cleffa, or Diglett — which is the best Madeleine?
Edit: Now that I think it, a team that has a Hippopotas or a Psyduck could absolutely hinder this set. Hippopotas will be able to change the weather from permanent Hail to permanent Sandstorm, then switch to something that can benefit from that weather. Hippopotas also has a high chance of using a Rock attack, that can totally kill Snover if it switches into it. However, Hippopotas can be killed off with Surf, if any one of the Surfers can safely switch. Golduck's only counter in this team is the Staryu with Thunderbolt.