An odd yet effective pairing is Rayquaza and Salamence. Despite the fact that the two have the same typing, and thus, the same weaknesses, the two form a phenomenal offensive partnership, able to lure out and defeat each others counters.
One particular Pokémon who should be on almost all Salamence + Rayquaza teams is Wobbuffet. Wobbuffet is able to aid both of their set ups via the use of Encore and will also eliminate most Choice Scarf users that can be a problem. Although a niche Pokémon in the Ubers metagame, Magnezone can be helpful to Salamence and Rayquaza by eliminating the Steel-types that can switch into their Dragon-type attacks. Magnezone will also lure in Fire-, Ground- and Fighting-type attacks for Salamence and Rayquaza to switch into. Groudon is useful for its ability to cause eternal sunshine, which is the more favorable weather for Salamence due to its boost to Fire Blast's power. Be warned, however, as this will have the side effect of making half your team weak to Ice-type attacks!
When using Salamence and Rayquaza together, Stealth Rock is almost necessary. This is because both Salamence and Rayquaza rely on Stealth Rock to gain several KOs, depending on the set. The pair is also weak to Stealth Rock, so it may prove useful to keep it off the field. Forretress stands out as an excellent choice here. Steel-types already make a great partner to Salamence and Rayquaza, and Forretress can use Rapid Spin to keep Stealth Rock off the field.
Another strategy is to keep Stealth Rock from ever being used in the first place. Choice Scarf Shaymin-S is an option here, however you again leave yourself vulnerable with 4x Ice weaknesses on half of your team. Choice Scarf Darkrai can put Deoxys-S and Deoxys-A to sleep before they set up Stealth Rock. Yet take care, as many Dialga and Groudon leads will carry a Chesto Berry to ensure that they either lay down Stealth Rock or paralyze Darkrai. Deoxys-S is the fastest user of Taunt in the game and thus can help out Salamence and Rayquaza by stopping the Stealth Rock attempts of slower leads. Deoxys-S is also a good user of Stealth Rock and can viably use Spikes if a Ghost-type is present on your team, although it should be noted that the best offensive spinblocker, Giratina-O, shares weaknesses with Salamence and Rayquaza.
There are several Pokémon who, while not being able to check Salamence and Rayquaza, will pose a threat to your team if you don't get the chance to set up. The biggest issue by far is Mewtwo. Mewtwo will outspeed and OHKO both Rayquaza and Salamence with Ice Beam if you have not attained a Dragon Dance. Mewtwo will become even more of an issue if you are using Wobbuffet, because Mewtwo can set up on it with Taunt and Calm Mind. Latias, Latios and Garchomp that lack Choice Scarf are going to be problems as well, because they all outspeed Salamence and Rayquaza, and will OHKO both with their STAB Dragon-type attacks. Life Orb Gengar will also outspeed Salamence and Rayquaza, and OHKO both with Icy Wind. While mixed Palkia must risk a Speed tie against Salamence, it will cause problems if it KOs Salamence. Because of these problems, Scizor makes a great teammate for both Salamence and Rayquaza. Scizor will be able to switch into Mewtwo's Ice Beams, Latias and Latios' Dragon-type attacks, and Gengar's Icy Wind. Scizor can then deal a large amount of damage to Mewtwo, Latias, and Latios with Pursuit as they flee, and crush Gengar with Bullet Punch. However, be wary of Fire-type attacks. Max HP Metagross can be a good alternative to Scizor because it is able to survive most Fire-type attacks in the rain. Choice Scarf Metagross can also be used to switch into Garchomp's Outrage and OHKO it with Ice Punch. A Careful Choice Band Tyranitar is particularly notable for being one of the most reliable users of Pursuit to beat Latias and Latios with, as only Grass Knot from Latios is guaranteed to 2HKO Tyranitar. However, the sandstorm can be a nuisance to Salamence, so carrying Kyogre and/or Groudon is recommended. Kyogre will usually be able to defeat Mewtwo (as long as it lacks Thunder or Grass Knot) and Gengar and has the option to use Thunder Wave to paralyze Latias, Latios and Palkia switch-ins. Although it's risky to use another Pokémon weak to Dragon- and Ice-type attacks, Latias and Latios are very good at revenge killing Palkia and Garchomp that lack Choice Scarf.
In Ubers, there are two main walls that give both of these Salamence sets problems: Timid Lugia and Cresselia. Timid Lugia will survive any of Mixed Salamence's assaults and then OHKO with Ice Beam. Timid Lugia will also defeat Dragon Dance Salamence as long as it is at near full health (taking 71.4% - 84.4% from a +1 Outrage, around a 79.5% chance of surviving after Stealth Rock damage and Leftovers recovery). Cresselia is able to survive any sort of attack from Salamence and then OHKO it with Ice Beam after Stealth Rock damage. Wobbuffet is a great partner for Salamence and Rayquaza in this case. Wobbuffet is able to use Encore to make both Lugia and Cresselia set-up bait for your other sweepers. If your Wobbuffet is carrying Tickle, it can be paired with a Pursuit user such as Scizor to eliminate Lugia and Cresselia from the battlefield. Scizor itself can switch into Cresselia with ease and then threaten to do a huge amount of damage to it with U-turn. Mewtwo is capable of using Taunt and Calm Mind to set up on both Lugia and Cresselia. In a similar manner, Darkrai can use Dark Void to put Lugia and Cresselia to sleep and threaten a sweep with Nasty Plot. Kyogre has no problems switching into Lugia and Cresselia's Ice Beams, and can threaten to smash them with its powerful, rain-boosted STAB Water-type attacks.
Salamence and Rayquaza will have problems with 3 priority users. The most common problem is Scizor. While Scizor is unable to OHKO either Salamence or Rayquaza, it's notable for its ability to pick both off when they are weakened. Scizor's Choice Banded Bullet Punch will always 2HKO both Salamence and Rayquaza after Stealth Rock damage, and Scizor can use its Dragon-type resistance to switch in on Outrage. Although uncommon, both Weavile and Mamoswine have the potential to be huge problems for Salamence and Rayquaza due to their STAB Ice Shard. Mewtwo makes a superb Scizor lure, as it can use Flamethrower and Fire Blast and also has the option of using Aura Sphere to revenge kill Mamoswine and Weavile. Dialga is notable for having a resistance to Bullet Punch and a neutrality to Ice Shard, and can fry both Scizor and Mamoswine with Fire Blast. Dialga also has the option of equipping a Choice Scarf to revenge kill Weavile. In a similar manner, Kyogre resists both Ice Shard and Bullet Punch. Kyogre can crush Scizor and Mamoswine with its insanely powerful Surfs and like Dialga, can equip a Choice Scarf to revenge kill Weavile. A Scizor of your own is capable of switching into Weavile and Mamoswine's Ice Shard and can smash them with Bullet Punch. Like Scizor, a Choice Scarf Jirachi can easily switch into Ice Shard and ram Weavile and Mamoswine with Iron Head.
Since Salamence and Rayquaza share each other's weaknesses, this means that your team will at least have two weaknesses to Rock-, Dragon-, and Ice-type attacks. This makes it almost required to have a Steel-type partner. Bronzong, Scizor, and Forretress are all great choices for this role. They resist Ice- and Dragon-type attacks (Bronzong in particular also resists Rock-type attacks), while Salamence and Rayquaza resist the Fire-type attacks aimed at them. Jirachi and Metagross are also superb teammates, as they resist all of Salamence and Rayquaza's weaknesses, and in return, Salamence and Rayquaza can switch into Ground- and Fire-type attacks. While Kyogre doesn't resist Dragon-type attacks, it does sport a useful Ice-type resistance and can lure in Grass-type attacks for Salamence or Rayquaza to switch into. Groudon provides a Rock-type resistance, and like Kyogre, can lure in Grass-type attacks for Salamence or Rayquaza to switch into. Dialga provides a Rock-type resistance, and it can lure in Fighting- and Ground-type attacks for Salamence or Rayquaza to switch into.
(everything but the first paragraph is taken from Salamence's Team Options page, but I feel it is necessary since it also deals with Rayquaza)
One particular Pokémon who should be on almost all Salamence + Rayquaza teams is Wobbuffet. Wobbuffet is able to aid both of their set ups via the use of Encore and will also eliminate most Choice Scarf users that can be a problem. Although a niche Pokémon in the Ubers metagame, Magnezone can be helpful to Salamence and Rayquaza by eliminating the Steel-types that can switch into their Dragon-type attacks. Magnezone will also lure in Fire-, Ground- and Fighting-type attacks for Salamence and Rayquaza to switch into. Groudon is useful for its ability to cause eternal sunshine, which is the more favorable weather for Salamence due to its boost to Fire Blast's power. Be warned, however, as this will have the side effect of making half your team weak to Ice-type attacks!
When using Salamence and Rayquaza together, Stealth Rock is almost necessary. This is because both Salamence and Rayquaza rely on Stealth Rock to gain several KOs, depending on the set. The pair is also weak to Stealth Rock, so it may prove useful to keep it off the field. Forretress stands out as an excellent choice here. Steel-types already make a great partner to Salamence and Rayquaza, and Forretress can use Rapid Spin to keep Stealth Rock off the field.
Another strategy is to keep Stealth Rock from ever being used in the first place. Choice Scarf Shaymin-S is an option here, however you again leave yourself vulnerable with 4x Ice weaknesses on half of your team. Choice Scarf Darkrai can put Deoxys-S and Deoxys-A to sleep before they set up Stealth Rock. Yet take care, as many Dialga and Groudon leads will carry a Chesto Berry to ensure that they either lay down Stealth Rock or paralyze Darkrai. Deoxys-S is the fastest user of Taunt in the game and thus can help out Salamence and Rayquaza by stopping the Stealth Rock attempts of slower leads. Deoxys-S is also a good user of Stealth Rock and can viably use Spikes if a Ghost-type is present on your team, although it should be noted that the best offensive spinblocker, Giratina-O, shares weaknesses with Salamence and Rayquaza.
There are several Pokémon who, while not being able to check Salamence and Rayquaza, will pose a threat to your team if you don't get the chance to set up. The biggest issue by far is Mewtwo. Mewtwo will outspeed and OHKO both Rayquaza and Salamence with Ice Beam if you have not attained a Dragon Dance. Mewtwo will become even more of an issue if you are using Wobbuffet, because Mewtwo can set up on it with Taunt and Calm Mind. Latias, Latios and Garchomp that lack Choice Scarf are going to be problems as well, because they all outspeed Salamence and Rayquaza, and will OHKO both with their STAB Dragon-type attacks. Life Orb Gengar will also outspeed Salamence and Rayquaza, and OHKO both with Icy Wind. While mixed Palkia must risk a Speed tie against Salamence, it will cause problems if it KOs Salamence. Because of these problems, Scizor makes a great teammate for both Salamence and Rayquaza. Scizor will be able to switch into Mewtwo's Ice Beams, Latias and Latios' Dragon-type attacks, and Gengar's Icy Wind. Scizor can then deal a large amount of damage to Mewtwo, Latias, and Latios with Pursuit as they flee, and crush Gengar with Bullet Punch. However, be wary of Fire-type attacks. Max HP Metagross can be a good alternative to Scizor because it is able to survive most Fire-type attacks in the rain. Choice Scarf Metagross can also be used to switch into Garchomp's Outrage and OHKO it with Ice Punch. A Careful Choice Band Tyranitar is particularly notable for being one of the most reliable users of Pursuit to beat Latias and Latios with, as only Grass Knot from Latios is guaranteed to 2HKO Tyranitar. However, the sandstorm can be a nuisance to Salamence, so carrying Kyogre and/or Groudon is recommended. Kyogre will usually be able to defeat Mewtwo (as long as it lacks Thunder or Grass Knot) and Gengar and has the option to use Thunder Wave to paralyze Latias, Latios and Palkia switch-ins. Although it's risky to use another Pokémon weak to Dragon- and Ice-type attacks, Latias and Latios are very good at revenge killing Palkia and Garchomp that lack Choice Scarf.
In Ubers, there are two main walls that give both of these Salamence sets problems: Timid Lugia and Cresselia. Timid Lugia will survive any of Mixed Salamence's assaults and then OHKO with Ice Beam. Timid Lugia will also defeat Dragon Dance Salamence as long as it is at near full health (taking 71.4% - 84.4% from a +1 Outrage, around a 79.5% chance of surviving after Stealth Rock damage and Leftovers recovery). Cresselia is able to survive any sort of attack from Salamence and then OHKO it with Ice Beam after Stealth Rock damage. Wobbuffet is a great partner for Salamence and Rayquaza in this case. Wobbuffet is able to use Encore to make both Lugia and Cresselia set-up bait for your other sweepers. If your Wobbuffet is carrying Tickle, it can be paired with a Pursuit user such as Scizor to eliminate Lugia and Cresselia from the battlefield. Scizor itself can switch into Cresselia with ease and then threaten to do a huge amount of damage to it with U-turn. Mewtwo is capable of using Taunt and Calm Mind to set up on both Lugia and Cresselia. In a similar manner, Darkrai can use Dark Void to put Lugia and Cresselia to sleep and threaten a sweep with Nasty Plot. Kyogre has no problems switching into Lugia and Cresselia's Ice Beams, and can threaten to smash them with its powerful, rain-boosted STAB Water-type attacks.
Salamence and Rayquaza will have problems with 3 priority users. The most common problem is Scizor. While Scizor is unable to OHKO either Salamence or Rayquaza, it's notable for its ability to pick both off when they are weakened. Scizor's Choice Banded Bullet Punch will always 2HKO both Salamence and Rayquaza after Stealth Rock damage, and Scizor can use its Dragon-type resistance to switch in on Outrage. Although uncommon, both Weavile and Mamoswine have the potential to be huge problems for Salamence and Rayquaza due to their STAB Ice Shard. Mewtwo makes a superb Scizor lure, as it can use Flamethrower and Fire Blast and also has the option of using Aura Sphere to revenge kill Mamoswine and Weavile. Dialga is notable for having a resistance to Bullet Punch and a neutrality to Ice Shard, and can fry both Scizor and Mamoswine with Fire Blast. Dialga also has the option of equipping a Choice Scarf to revenge kill Weavile. In a similar manner, Kyogre resists both Ice Shard and Bullet Punch. Kyogre can crush Scizor and Mamoswine with its insanely powerful Surfs and like Dialga, can equip a Choice Scarf to revenge kill Weavile. A Scizor of your own is capable of switching into Weavile and Mamoswine's Ice Shard and can smash them with Bullet Punch. Like Scizor, a Choice Scarf Jirachi can easily switch into Ice Shard and ram Weavile and Mamoswine with Iron Head.
Since Salamence and Rayquaza share each other's weaknesses, this means that your team will at least have two weaknesses to Rock-, Dragon-, and Ice-type attacks. This makes it almost required to have a Steel-type partner. Bronzong, Scizor, and Forretress are all great choices for this role. They resist Ice- and Dragon-type attacks (Bronzong in particular also resists Rock-type attacks), while Salamence and Rayquaza resist the Fire-type attacks aimed at them. Jirachi and Metagross are also superb teammates, as they resist all of Salamence and Rayquaza's weaknesses, and in return, Salamence and Rayquaza can switch into Ground- and Fire-type attacks. While Kyogre doesn't resist Dragon-type attacks, it does sport a useful Ice-type resistance and can lure in Grass-type attacks for Salamence or Rayquaza to switch into. Groudon provides a Rock-type resistance, and like Kyogre, can lure in Grass-type attacks for Salamence or Rayquaza to switch into. Dialga provides a Rock-type resistance, and it can lure in Fighting- and Ground-type attacks for Salamence or Rayquaza to switch into.
(everything but the first paragraph is taken from Salamence's Team Options page, but I feel it is necessary since it also deals with Rayquaza)
