I have created a stall team which I usually win battles with. This team has all defensive pokemon, each serving a unique purpose. Because they are all defensive, my battles are usually very long and focus on keeping my pokemon alive while slowly taking out my opponent's pokemon (basically a dedicated stall team). Battles are typically 50-100 turns (can be much longer occasionally though).
The main problems I have with my team are dealing with Calm Mind users, steel types, and pokemon that use Secret Sword/Psyshock.
Here is my team (Gliscor, Venusaur, Blissey, Goodra, Quagsire, Heatran):
Gliscor (244 HP, 192 SpDef, 72 Spd)
Item: Toxic Orb
Ability: Poison Heal
Nature: Calm (+SpDef, -SpAtk)
Taunt
Roost
Toxic
Knock Off
Gliscor is probably my MVP on this team. The EV's and nature are inclined towards special defense so he is a mixed wall. He can take pretty much any neutral hit well and heal damage with Roost and Poison Heal. Taunt allows Gliscor to be incredibly annoying to most defensive pokemon thanks to his good speed (for a defensive pokemon), defensive stats, and amazing ability to recover health. Toxic is used to dwindle opposing pokemon's health. Knock Off is used as an easy prediction move to remove items from pokemon. I really like Knock Off because stalling is easier against pokemon without items.
I usually lead with Gliscor to activate Poison Heal right away. Most of the time when I lose, Gliscor is generally taken out early. This happens because Gliscor is a very important part of my defensive core.
Venusaur (252 HP, 240 Def, 16 Spd)
Item: Venusaurite
Ability: Chlorophyll (Thick Fat)
Nature: Bold (+Def, -Atk)
Giga Drain
Sludge Bomb
Sleep Powder
Synthesis
Venusaur is one of my physical walls. When I do not lead with Gliscor, I will probably lead with Venusaur (to mega evolve right away). Giga Drain and Sludge Bomb are conventional attacking moves for Venusaur. Sleep Powder is great for temporarily eliminating an opposing pokemon (and annoying my opponent). Synthesis is mandatory to keep Venusaur alive longer.
Once Venusaur mega evolves, he can take any attack well besides flying and psychic ones (Thick Fat neutralizes super effectiveness of fire and ice moves). Venusaur is my only answer to Keldeo (the pokemon I hate facing the most with this team). He can also counter many offensive threats, and is immune to sleep and poison status. I have tried replacing Sleep Powder with Earthquake and Hidden Power Fire, but I find they are too situational and I like putting an opposing pokemon to sleep to mess with my opponent's momentum.
Blissey (4 HP, 252 Def, 252 Sp.Def)
Item: Leftovers
Ability: Natural Cure
Nature: Calm (+Sp.Def, -Atk)
Wish
Soft-Boiled
Toxic
Fire Blast
Blissey is obviously my team's healer and a special wall. I chose Blissey over Chansey for three reasons. Blissey can heal with leftovers, Blissey is not as crippled by Knock Off, and Blissey can surprise steel types with Fire Blast. I use a Calm nature instead of a Bold nature because the 10% boost is so much more signifcant for special defense. I max EV's for both defenses because I still want Blissey to stand a chance against some physical moves.
Blissey obviously tanks special hits like a champ. Also, wish can almost fully heal most of my other pokemon (which is super important for a team that wants a really long battle). Once again, spreading around Toxic is necessary for damaging my opponent. Fire Blast is particularly great for Scizor and Ferrothorn.
I do not have Heal Bell because I do not want to remove Gliscor's status. Also my team is not too bad against status moves (Gliscor should always be poisoned, Venusaur cannot be poisoned or put to sleep, Blissey has Natural Cure, Heatran cannot be burned or poisoned). I thing I have not tried is replacing Soft-Boiled with Protect. My only problem with this is I may run out of PP for Wish.
Goodra (232 HP, 252 Sp.Atk, 8 Sp.Def, 16 Spd)
Item: Assault Vest
Ability: Sap Sipper
Nature: Modest (+Sp.Atk, -Atk)
Draco Meteor
Fire Blast
Thunderbolt
Dragon Tail
Goodra is really the only offense I have on this team. Like Blissey, Goodra is an amazing special wall (especially with Assault Vest). Since Goodra has no recovery moves, it relies a lot on Wish from Blissey.
The attacking moves put offensive pressure on my opponent, while Dragon Tail phazes pokemon to increase damage from Stealth Rock. The 16 speed EVs allow Goodra to outspeed max speed Adamant Azumarill.
Goodra is the newest addition on this team. I added him because he can take special hits really well (a Choice Specs Latios cannot OHKO Goodra with Draco Meteor, which is super effective). Also, he is immune to Spore because of Sap Sipper. Between Goodra and Blissey, the only special moves that can do much are those that target physical defense.
I am open to replacing Goodra with another pokemon. Some possible ideas are Starmie (rapid spin support) and Florges (special wall with recovery and extra wish support). I think Goodra works better on this team though because Stealth Rock is not that harmful to my team, and I already have a lot of healing on this team.
Quagsire (252 HP, 252 Def, 4 Sp.Def)
Item: Leftovers
Ability: Unaware
Nature: Relaxed (+Def, -Spd)
Scald
Earthquake
Recover
Toxic
Quagsire is my other dedicated physical wall. While Venusaur has better defensive stats, Quagsire has Unaware. This is essential to stopping physical boosting sweepers. Because my team provides very little offensive pressure, it is very easy for opponents to get at least one boost. However, Quagsire doesn't care about stat boosting (it is hilarious when opponents keep on boosting against Quagsire). Scald and Toxic can do damage/inflict status. Earthquake is my most used attacking move. Recover is for obvious recovery.
Even though Quagsire has mediocre defensive stats, his typing is very good for my defensive team. His only weakness is Grass, which is covered very well by my other pokemon (one immunity, two double resistances). Also, being able to use recover for stalling makes Quagsire very ideal. I use a Relaxed nature instead of an Impish nature to prevent reduction in Scald's damage output.
Heatran (248 HP, 216 Sp.Def, 44 Spd)
Item: Leftovers
Ability: Flash Fire
Nature: Calm (+Sp.Def, -Atk)
Lava Plume
Taunt
Protect
Stealth Rock
Heatran is my lead whenever Gliscor and Venusaur are not because he can use Taunt and Stealth Rock. Having a second Taunt user increases annoyingness of my team, and Heatran can completely shut down Fairy pokemon with Taunt. Protect is for scouting, accumulating more Leftovers recovery, and accumulating more Toxic damage on opponents. I used to have Toxic instead of Stealth Rock (I had a Ferrothorn instead of Goodra which used Stealth Rock), but Ferrothorn was not super neccessary. I also tried having Stealth Rock on Blissey, but offering healing support and Stealth Rock was too much for one pokemon.
Heatran is another specially defensive pokemon. With his fantastic typing, he can counter many pokemon (defensive ones in particular). Protect is not only great for scouting, but also for wasting opposing pokemon's PP (great for Hydro Pump). When I damage opposing pokemon, Protect can help me determine whether some of them are holding a choice item, which is very useful for prediction.
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General Notes
This team has had a good amount of success. Any suggestions for improvement would be appreciated.
The main problems I have with my team are dealing with Calm Mind users, steel types, and pokemon that use Secret Sword/Psyshock.
Here is my team (Gliscor, Venusaur, Blissey, Goodra, Quagsire, Heatran):

Gliscor (244 HP, 192 SpDef, 72 Spd)
Item: Toxic Orb
Ability: Poison Heal
Nature: Calm (+SpDef, -SpAtk)
Taunt
Roost
Toxic
Knock Off
Gliscor is probably my MVP on this team. The EV's and nature are inclined towards special defense so he is a mixed wall. He can take pretty much any neutral hit well and heal damage with Roost and Poison Heal. Taunt allows Gliscor to be incredibly annoying to most defensive pokemon thanks to his good speed (for a defensive pokemon), defensive stats, and amazing ability to recover health. Toxic is used to dwindle opposing pokemon's health. Knock Off is used as an easy prediction move to remove items from pokemon. I really like Knock Off because stalling is easier against pokemon without items.
I usually lead with Gliscor to activate Poison Heal right away. Most of the time when I lose, Gliscor is generally taken out early. This happens because Gliscor is a very important part of my defensive core.

Venusaur (252 HP, 240 Def, 16 Spd)
Item: Venusaurite
Ability: Chlorophyll (Thick Fat)
Nature: Bold (+Def, -Atk)
Giga Drain
Sludge Bomb
Sleep Powder
Synthesis
Venusaur is one of my physical walls. When I do not lead with Gliscor, I will probably lead with Venusaur (to mega evolve right away). Giga Drain and Sludge Bomb are conventional attacking moves for Venusaur. Sleep Powder is great for temporarily eliminating an opposing pokemon (and annoying my opponent). Synthesis is mandatory to keep Venusaur alive longer.
Once Venusaur mega evolves, he can take any attack well besides flying and psychic ones (Thick Fat neutralizes super effectiveness of fire and ice moves). Venusaur is my only answer to Keldeo (the pokemon I hate facing the most with this team). He can also counter many offensive threats, and is immune to sleep and poison status. I have tried replacing Sleep Powder with Earthquake and Hidden Power Fire, but I find they are too situational and I like putting an opposing pokemon to sleep to mess with my opponent's momentum.

Blissey (4 HP, 252 Def, 252 Sp.Def)
Item: Leftovers
Ability: Natural Cure
Nature: Calm (+Sp.Def, -Atk)
Wish
Soft-Boiled
Toxic
Fire Blast
Blissey is obviously my team's healer and a special wall. I chose Blissey over Chansey for three reasons. Blissey can heal with leftovers, Blissey is not as crippled by Knock Off, and Blissey can surprise steel types with Fire Blast. I use a Calm nature instead of a Bold nature because the 10% boost is so much more signifcant for special defense. I max EV's for both defenses because I still want Blissey to stand a chance against some physical moves.
Blissey obviously tanks special hits like a champ. Also, wish can almost fully heal most of my other pokemon (which is super important for a team that wants a really long battle). Once again, spreading around Toxic is necessary for damaging my opponent. Fire Blast is particularly great for Scizor and Ferrothorn.
I do not have Heal Bell because I do not want to remove Gliscor's status. Also my team is not too bad against status moves (Gliscor should always be poisoned, Venusaur cannot be poisoned or put to sleep, Blissey has Natural Cure, Heatran cannot be burned or poisoned). I thing I have not tried is replacing Soft-Boiled with Protect. My only problem with this is I may run out of PP for Wish.

Goodra (232 HP, 252 Sp.Atk, 8 Sp.Def, 16 Spd)
Item: Assault Vest
Ability: Sap Sipper
Nature: Modest (+Sp.Atk, -Atk)
Draco Meteor
Fire Blast
Thunderbolt
Dragon Tail
Goodra is really the only offense I have on this team. Like Blissey, Goodra is an amazing special wall (especially with Assault Vest). Since Goodra has no recovery moves, it relies a lot on Wish from Blissey.
The attacking moves put offensive pressure on my opponent, while Dragon Tail phazes pokemon to increase damage from Stealth Rock. The 16 speed EVs allow Goodra to outspeed max speed Adamant Azumarill.
Goodra is the newest addition on this team. I added him because he can take special hits really well (a Choice Specs Latios cannot OHKO Goodra with Draco Meteor, which is super effective). Also, he is immune to Spore because of Sap Sipper. Between Goodra and Blissey, the only special moves that can do much are those that target physical defense.
I am open to replacing Goodra with another pokemon. Some possible ideas are Starmie (rapid spin support) and Florges (special wall with recovery and extra wish support). I think Goodra works better on this team though because Stealth Rock is not that harmful to my team, and I already have a lot of healing on this team.

Quagsire (252 HP, 252 Def, 4 Sp.Def)
Item: Leftovers
Ability: Unaware
Nature: Relaxed (+Def, -Spd)
Scald
Earthquake
Recover
Toxic
Quagsire is my other dedicated physical wall. While Venusaur has better defensive stats, Quagsire has Unaware. This is essential to stopping physical boosting sweepers. Because my team provides very little offensive pressure, it is very easy for opponents to get at least one boost. However, Quagsire doesn't care about stat boosting (it is hilarious when opponents keep on boosting against Quagsire). Scald and Toxic can do damage/inflict status. Earthquake is my most used attacking move. Recover is for obvious recovery.
Even though Quagsire has mediocre defensive stats, his typing is very good for my defensive team. His only weakness is Grass, which is covered very well by my other pokemon (one immunity, two double resistances). Also, being able to use recover for stalling makes Quagsire very ideal. I use a Relaxed nature instead of an Impish nature to prevent reduction in Scald's damage output.

Heatran (248 HP, 216 Sp.Def, 44 Spd)
Item: Leftovers
Ability: Flash Fire
Nature: Calm (+Sp.Def, -Atk)
Lava Plume
Taunt
Protect
Stealth Rock
Heatran is my lead whenever Gliscor and Venusaur are not because he can use Taunt and Stealth Rock. Having a second Taunt user increases annoyingness of my team, and Heatran can completely shut down Fairy pokemon with Taunt. Protect is for scouting, accumulating more Leftovers recovery, and accumulating more Toxic damage on opponents. I used to have Toxic instead of Stealth Rock (I had a Ferrothorn instead of Goodra which used Stealth Rock), but Ferrothorn was not super neccessary. I also tried having Stealth Rock on Blissey, but offering healing support and Stealth Rock was too much for one pokemon.
Heatran is another specially defensive pokemon. With his fantastic typing, he can counter many pokemon (defensive ones in particular). Protect is not only great for scouting, but also for wasting opposing pokemon's PP (great for Hydro Pump). When I damage opposing pokemon, Protect can help me determine whether some of them are holding a choice item, which is very useful for prediction.
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General Notes
- none of my pokemon are weak to Stealth Rock, and most of them can easily recover Stealth Rock damage
- status is not a big issue for my team
- boosting sweepers can be stopped (Quagsire for physical ones, Blissey and/or Goodra for special ones) except for Calm Mind users with Secret Sword/Psyshock (Venusaur can only counter Keldeo if it has over half health, no one else on my team can counter him)
- my team has issues defeating steel types (Fire Blast is really my only way of beating most of them)
- Fairy types do not threaten my team (Venusaur and Heatran own them)
This team has had a good amount of success. Any suggestions for improvement would be appreciated.