Title says it all... at first I wanted to make a decent lead for a team but since Team Preview will probably make you scramble the order of your team, what the heck and just use what fits the team well. Though if anything, Gastrodon will be my lead of choice against weather teams (except hail), which are about half of all teams.

Gastrodon (F) @Leftovers
EVs: 252 HP / 4 Sp Atk / 252 Sp Def
Nature: Sassy
Ability: Storm Drain
~ Scald
~ Earthquake
~ Toxic
~ Recover
I seriously can't help but be heads over heels over Gastrodon. Matches up pretty well against Tyranitar and Hippowdon who can't do much to Gastrodon while Gastrodon can threaten a burn with Scald. Politoed will barely scratch it since it's STAB Water attacks can't touch Gastrodon due to Storm Drain, while Gastrodon can just Recover off the damage, assuming that it's the Choiced variants without Toxic. Gastrodon can even survive Energy Ball (Though in this case it's more prudent to switch out) from Life Orb Ninetales to KO back with Earthquake. Of course, Abomasnow is a problem but that is what your teammates are for. Not that weather really matters as I don't use it myself and therfore there won't be weather wars but point is, most people lead with their weather starter and most of them lose to Gastrodon. Weather aside, Gastrodon is still incredibly bulky, he can even survive a Life Orbbed Draco Meteor from Latios and Recover off the damage and proceed to Toxic-stall Latios.

Scizor (F) @Leftovers
EVs: 252 HP / 40 Atk / 216 Sp Def
Nature: Adamant
Ability: Technician
~ Swords Dance
~ Bullet Punch
~ Bug Bite
~ Roost
Of course, something that can do something about those Grass types that plague Gastrodon is a must, and Scizor fits the bill very nicely. The fact that Gastrodon resists Scizor's Fire weakness only gives me more of a reason to use Scizor here. I originally wanted to use the Choice Band set with U-turn, but I personally prefer longevity, and thus I use the Defensive Swords Dance set which can clean up in mid to late-game. Of course, if someone can persuade me to use the Choice Band set over this, I'm all ears.

Volcarona (F) @Life Orb
EVs: 252 Sp Atk / 4 Sp Def / 252 Spe
Nature: Timid
Ability: Flame Body
~ Quiver Dance
~ Fiery Dance
~ Bug Buzz
~ Hidden Power [Rock]
I need a little more offense in my team, preferably special attacks since Scizor is already covering the physical side, so I decided to use the offensive Volcarona. The lack of longevity may be a disadvantage at times, but unlike Scizor, Volcarona doesn't exactly have an excellent typing nor recovery that is not dependant on weather, and therefore I believe the more offensive Quiver Dance set would be more well-suited. Volcarona can also break through Pokemon like Jirachi, Bronzong and Skarmory which give Scizor a lot of trouble, while Scizor returns the favour by being able to eliminate Chansey and Blissey which for obvious reasons give Volcarona a lot of trouble.

Ferrothorn (F) @Leftovers
EVs: 252 HP / 48 Def / 208 Sp Def
Nature: Relaxed
Ability: Iron Barbs
~ Spikes
~ Power Whip
~ Gyro Ball
~ Leech Seed
Of course, what sort of team doesn't have entry hazards? Volcarona can use entry hazards to get around Focus Sashes, and so can Scizor. Ferrothorn can easily supply Spikes with its numerous resistances and superb defenses. Power Whip and Gyro Ball are standard attacks, while Leech Seed is for recovery.
Donphan (F) @Leftovers
EVs: 252 HP / 252 Atk / 4 Def
Nature: Adamant
Ability: Sturdy
~ Stealth Rock
~ Rapid Spin
~ Earthquake
~ Ice Shard
Oh wait, no Stealth Rock? No Spinners as well? Volcarona will definitely need a teammate that can spin away Stealth Rock, otherwise it will be losing half its health when it switches in. Donphan fits the bill by also being able to set up Stealth Rock itself, while being able to hit back hard with STAB Earthquake from 372 Attack. Ice Shard is there for priority and to finish off weakened Pokemon, or 4x weak Dragons.

Jellicent (F) @Leftovers
EVs: 252 HP / 216 Def / 44 Sp Def
Nature: Bold
Ability: Water Absorb
~ Scald
~ Will-o-Wisp
~ Taunt
~ Recover
If I'm going to use Spikes and Stealth Rock, naturally I need a spinblocker. Jellicent works pretty well since it has great synergy with Ferrothorn. Moves are pretty self-explanatory.
Anyway... any suggestions for improvement? I noticed my team does not have any Flying resists, if there's something like Choice Banded Staraptor with Brave Bird, I'm screwed. Furthermore, Volcarona will not be so useful against rain teams as one of its STAB attacks will be halved in power. But if I replace anything, I will probably lose some of the usefulness of that particular Pokemon. Still, I'm no expert, and I can certainly use some suggestions for improvement.

Gastrodon (F) @Leftovers
EVs: 252 HP / 4 Sp Atk / 252 Sp Def
Nature: Sassy
Ability: Storm Drain
~ Scald
~ Earthquake
~ Toxic
~ Recover
I seriously can't help but be heads over heels over Gastrodon. Matches up pretty well against Tyranitar and Hippowdon who can't do much to Gastrodon while Gastrodon can threaten a burn with Scald. Politoed will barely scratch it since it's STAB Water attacks can't touch Gastrodon due to Storm Drain, while Gastrodon can just Recover off the damage, assuming that it's the Choiced variants without Toxic. Gastrodon can even survive Energy Ball (Though in this case it's more prudent to switch out) from Life Orb Ninetales to KO back with Earthquake. Of course, Abomasnow is a problem but that is what your teammates are for. Not that weather really matters as I don't use it myself and therfore there won't be weather wars but point is, most people lead with their weather starter and most of them lose to Gastrodon. Weather aside, Gastrodon is still incredibly bulky, he can even survive a Life Orbbed Draco Meteor from Latios and Recover off the damage and proceed to Toxic-stall Latios.

Scizor (F) @Leftovers
EVs: 252 HP / 40 Atk / 216 Sp Def
Nature: Adamant
Ability: Technician
~ Swords Dance
~ Bullet Punch
~ Bug Bite
~ Roost
Of course, something that can do something about those Grass types that plague Gastrodon is a must, and Scizor fits the bill very nicely. The fact that Gastrodon resists Scizor's Fire weakness only gives me more of a reason to use Scizor here. I originally wanted to use the Choice Band set with U-turn, but I personally prefer longevity, and thus I use the Defensive Swords Dance set which can clean up in mid to late-game. Of course, if someone can persuade me to use the Choice Band set over this, I'm all ears.

Volcarona (F) @Life Orb
EVs: 252 Sp Atk / 4 Sp Def / 252 Spe
Nature: Timid
Ability: Flame Body
~ Quiver Dance
~ Fiery Dance
~ Bug Buzz
~ Hidden Power [Rock]
I need a little more offense in my team, preferably special attacks since Scizor is already covering the physical side, so I decided to use the offensive Volcarona. The lack of longevity may be a disadvantage at times, but unlike Scizor, Volcarona doesn't exactly have an excellent typing nor recovery that is not dependant on weather, and therefore I believe the more offensive Quiver Dance set would be more well-suited. Volcarona can also break through Pokemon like Jirachi, Bronzong and Skarmory which give Scizor a lot of trouble, while Scizor returns the favour by being able to eliminate Chansey and Blissey which for obvious reasons give Volcarona a lot of trouble.

Ferrothorn (F) @Leftovers
EVs: 252 HP / 48 Def / 208 Sp Def
Nature: Relaxed
Ability: Iron Barbs
~ Spikes
~ Power Whip
~ Gyro Ball
~ Leech Seed
Of course, what sort of team doesn't have entry hazards? Volcarona can use entry hazards to get around Focus Sashes, and so can Scizor. Ferrothorn can easily supply Spikes with its numerous resistances and superb defenses. Power Whip and Gyro Ball are standard attacks, while Leech Seed is for recovery.

Donphan (F) @Leftovers
EVs: 252 HP / 252 Atk / 4 Def
Nature: Adamant
Ability: Sturdy
~ Stealth Rock
~ Rapid Spin
~ Earthquake
~ Ice Shard
Oh wait, no Stealth Rock? No Spinners as well? Volcarona will definitely need a teammate that can spin away Stealth Rock, otherwise it will be losing half its health when it switches in. Donphan fits the bill by also being able to set up Stealth Rock itself, while being able to hit back hard with STAB Earthquake from 372 Attack. Ice Shard is there for priority and to finish off weakened Pokemon, or 4x weak Dragons.

Jellicent (F) @Leftovers
EVs: 252 HP / 216 Def / 44 Sp Def
Nature: Bold
Ability: Water Absorb
~ Scald
~ Will-o-Wisp
~ Taunt
~ Recover
If I'm going to use Spikes and Stealth Rock, naturally I need a spinblocker. Jellicent works pretty well since it has great synergy with Ferrothorn. Moves are pretty self-explanatory.
Anyway... any suggestions for improvement? I noticed my team does not have any Flying resists, if there's something like Choice Banded Staraptor with Brave Bird, I'm screwed. Furthermore, Volcarona will not be so useful against rain teams as one of its STAB attacks will be halved in power. But if I replace anything, I will probably lose some of the usefulness of that particular Pokemon. Still, I'm no expert, and I can certainly use some suggestions for improvement.