Comments: I've been experimenting a lot with teams lately and this is one of my first jabs at a team strategy.
Dual Screen Sweep
Team at a Glance:
In Depth Look:
The Anti-Lead
Lucario (M) @ Focus Sash
Nature: Lonely
Ability: Inner Focus
EVs: 4 HP / 252 Atk / 252 Spe
-Close Combat
-Extreme Speed
-Crunch
-Counter
I chose Lucario as my lead pokemon to hopefully KO one opposing pokemon before dying. I don't plan on my Lucario dying and usually switch out to Cresselia when Focus Sash activates or Lucario is going to die next turn. Close Combat is a powerful STAB move that is very good against steel type leads and others in general. Extreme Speed is to KO Focus Sash users. Crunch is to take care of Psychic or Ghost types. Counter is a powerful option that is often useful. The ability Inner Focus stops users of Fake Out cold, preserving my Focus Sash.
The Dual Screen
Cresselia (F) @ Light Clay
Nature: Bold
Ability: Levitate
EVs: 252 HP / 60 Def / 152 Spe
-Reflect
-Light Screen
-Lunar Dance
-Thunder Wave
Right before Lucario dies I will usually switch out to Cresselia. Thunder Wave is a good option to paralyze an opposing pokemon and buy some time. I use Reflect and Light Screen as fast as I can and once that is said and done I Lunar Dance back to Lucario. Once I am back to Lucario I get my Anti-Lead all over again. Hopefully my opponent won't anticipate Lucario and use a ground move since Cresselia has Levitate. Focus Sash won't activate again unfortunately but Dual Screen will give some survivability to Lucario. Maybe I could replace Counter with something else on Lucario so that it has better type coverage such as Stone Edge so after I Lunar Dance I have more options for sweeping.
The DD Physical Sweeper
Gyarados (M) @ Life Orb
Nature: Adamant
Ability: Intimidate
EVs: 4 HP / 252 Atk / 252 Spe
-Dragon Dance
-Waterfall
-Ice Fang
-Stone Edge
When my rejuvenated Lucario goes out I will have to basically choose one of my three sweepers to go to. If the pokemon that killed Lucario was particularly a master of fire or ground type moves then Gyrados can switch in easier and perhaps Dragon Dance on the switch. After that it is a lethal sweeper only with Dual Screens making it more difficult than usual to take down. If a serious electric attack becomes a threat then I can switch over to Jolteon, who works with Gyarados to cover weaknesses. Waterfall is a reliable STAB attack. Ice Fang takes care of any dragon or ground type that tries to stop the sweep and Stone Edge is for neutral damage against water types mostly. Reflect + Intimidate should make life even harder for physical attackers.
The Mixed Sweeper
Salamence (M) @ Life Orb
Nature: Mild
Ability: Intimidate
EVs: 84 Atk / 216 SpA / 208
-Draco Meteor
-Earthquake
-Fire Blast
-Outrage
Salamence is a very reliable pokemon. I can use him after Lucario goes out if I don't have another option or later on in the game with ease. Draco Meteor is a very powerful one time dragon STAB attack. Fire Blast will take out steel types that resist dragon type moves. Earthquake is another option for steel types and if I happen to hit a switched in steel pokemon with Draco Meteor then I can simply use Earthquake (and not Fire Blast) to get rid of it. Outrage will usually be the final rampage out after Draco Meteor is used. Reflect + Intimidate should make life even harder for physical attackers.
The Nasty Plot Sweeper
Infernape (M) @ Life Orb
Nature: Naive
Ability: Blaze
EVs: 64 Atk / 252 SpA / 192 Spe
-Nasty Plot
-Flamethrower
-Close Combat
-Grass Knot
Infernape is another pokemon I can choose after Lucario dies. If Infernape is targeted with a ground move I can switch to Salamence of Gyrados. Infernape is often good to bring in against slower pokemon assuming they don't have a supereffective move. I will Nasty Plot if I have time, which hopefully dual screens will help with. After that Flamethrower gives me a reliable fire STAB attack and Close Combat gives me a reliable fighting STAB attack. Grass Knot is for water types mostly.
The Special Choice
Jolteon (M) @ Choice Specs
Nature: Timid
Ability: Volt Absorb
EVs: 4 HP / 252 SpA / 252 Spe
-Thunderbolt
-Shadow Ball
-Hidden Power Grass
-Baton Pass
I suck at this game really badly and Jolteon has saved me many times at the end of the game with his excellent neutral coverage. It isn't very often that I'll be down a couple pokemon and send this guy in to sweep away my opponent's last two or three pokemon in a dramatic turn of events. If a ground move is aimed at Jolteon then he can switch out to Gyarados or Salamence. Thunderbolt is the obvious STAB move. Shadow Ball gives good coverage and is good against Ghosts and Psychics. Hidden Power Grass is for things like Swampert and might help against a rock type.
This team has a stealth rock weakness. I could maybe have something switch in for Salamence like Latias. Whatever I do I don't want it to be too reactionary. Latias would stack dragon types and increase a weakness to ice moves. I could opt for a metal type pokemon like Metagross or Scizor, but increase my ground weakness. I like my team to be very threatening even if that opens up a weakness, as long as it is reasonable. I have never really seen a Dual Screen team so I'm not sure if there is a better way to use a Dual Screen setup. I have a lot of ground weaknesses but also three immunities to ground which can be used to an advantage. If Cresselia isn't going to get to Lunar Dance for some reason then my plan is weakened quite a bit and I'll have to rely on a sweeping army for the rest of the game to hold on. I'm still learning a lot about the game and look forward to insightful advice and explanations. Thanks.
Dual Screen Sweep
Team at a Glance:






In Depth Look:

The Anti-Lead
Lucario (M) @ Focus Sash
Nature: Lonely
Ability: Inner Focus
EVs: 4 HP / 252 Atk / 252 Spe
-Close Combat
-Extreme Speed
-Crunch
-Counter
I chose Lucario as my lead pokemon to hopefully KO one opposing pokemon before dying. I don't plan on my Lucario dying and usually switch out to Cresselia when Focus Sash activates or Lucario is going to die next turn. Close Combat is a powerful STAB move that is very good against steel type leads and others in general. Extreme Speed is to KO Focus Sash users. Crunch is to take care of Psychic or Ghost types. Counter is a powerful option that is often useful. The ability Inner Focus stops users of Fake Out cold, preserving my Focus Sash.

The Dual Screen
Cresselia (F) @ Light Clay
Nature: Bold
Ability: Levitate
EVs: 252 HP / 60 Def / 152 Spe
-Reflect
-Light Screen
-Lunar Dance
-Thunder Wave
Right before Lucario dies I will usually switch out to Cresselia. Thunder Wave is a good option to paralyze an opposing pokemon and buy some time. I use Reflect and Light Screen as fast as I can and once that is said and done I Lunar Dance back to Lucario. Once I am back to Lucario I get my Anti-Lead all over again. Hopefully my opponent won't anticipate Lucario and use a ground move since Cresselia has Levitate. Focus Sash won't activate again unfortunately but Dual Screen will give some survivability to Lucario. Maybe I could replace Counter with something else on Lucario so that it has better type coverage such as Stone Edge so after I Lunar Dance I have more options for sweeping.

The DD Physical Sweeper
Gyarados (M) @ Life Orb
Nature: Adamant
Ability: Intimidate
EVs: 4 HP / 252 Atk / 252 Spe
-Dragon Dance
-Waterfall
-Ice Fang
-Stone Edge
When my rejuvenated Lucario goes out I will have to basically choose one of my three sweepers to go to. If the pokemon that killed Lucario was particularly a master of fire or ground type moves then Gyrados can switch in easier and perhaps Dragon Dance on the switch. After that it is a lethal sweeper only with Dual Screens making it more difficult than usual to take down. If a serious electric attack becomes a threat then I can switch over to Jolteon, who works with Gyarados to cover weaknesses. Waterfall is a reliable STAB attack. Ice Fang takes care of any dragon or ground type that tries to stop the sweep and Stone Edge is for neutral damage against water types mostly. Reflect + Intimidate should make life even harder for physical attackers.

The Mixed Sweeper
Salamence (M) @ Life Orb
Nature: Mild
Ability: Intimidate
EVs: 84 Atk / 216 SpA / 208
-Draco Meteor
-Earthquake
-Fire Blast
-Outrage
Salamence is a very reliable pokemon. I can use him after Lucario goes out if I don't have another option or later on in the game with ease. Draco Meteor is a very powerful one time dragon STAB attack. Fire Blast will take out steel types that resist dragon type moves. Earthquake is another option for steel types and if I happen to hit a switched in steel pokemon with Draco Meteor then I can simply use Earthquake (and not Fire Blast) to get rid of it. Outrage will usually be the final rampage out after Draco Meteor is used. Reflect + Intimidate should make life even harder for physical attackers.

The Nasty Plot Sweeper
Infernape (M) @ Life Orb
Nature: Naive
Ability: Blaze
EVs: 64 Atk / 252 SpA / 192 Spe
-Nasty Plot
-Flamethrower
-Close Combat
-Grass Knot
Infernape is another pokemon I can choose after Lucario dies. If Infernape is targeted with a ground move I can switch to Salamence of Gyrados. Infernape is often good to bring in against slower pokemon assuming they don't have a supereffective move. I will Nasty Plot if I have time, which hopefully dual screens will help with. After that Flamethrower gives me a reliable fire STAB attack and Close Combat gives me a reliable fighting STAB attack. Grass Knot is for water types mostly.

The Special Choice
Jolteon (M) @ Choice Specs
Nature: Timid
Ability: Volt Absorb
EVs: 4 HP / 252 SpA / 252 Spe
-Thunderbolt
-Shadow Ball
-Hidden Power Grass
-Baton Pass
I suck at this game really badly and Jolteon has saved me many times at the end of the game with his excellent neutral coverage. It isn't very often that I'll be down a couple pokemon and send this guy in to sweep away my opponent's last two or three pokemon in a dramatic turn of events. If a ground move is aimed at Jolteon then he can switch out to Gyarados or Salamence. Thunderbolt is the obvious STAB move. Shadow Ball gives good coverage and is good against Ghosts and Psychics. Hidden Power Grass is for things like Swampert and might help against a rock type.
This team has a stealth rock weakness. I could maybe have something switch in for Salamence like Latias. Whatever I do I don't want it to be too reactionary. Latias would stack dragon types and increase a weakness to ice moves. I could opt for a metal type pokemon like Metagross or Scizor, but increase my ground weakness. I like my team to be very threatening even if that opens up a weakness, as long as it is reasonable. I have never really seen a Dual Screen team so I'm not sure if there is a better way to use a Dual Screen setup. I have a lot of ground weaknesses but also three immunities to ground which can be used to an advantage. If Cresselia isn't going to get to Lunar Dance for some reason then my plan is weakened quite a bit and I'll have to rely on a sweeping army for the rest of the game to hold on. I'm still learning a lot about the game and look forward to insightful advice and explanations. Thanks.