I've used Gastrodon a lot, specially at the beginning of BW2, but things have changed quite a bit so any input would be nice. Main changes in the current analysis would be stop mentioning Quagsire.
Gastrodon
[Overview]
<p>Gastrodon is a Pokemon blessed in both typing and ability, boasting two immunities, four resistances and a lone 4x weakness to Grass-type attacks. As if that wasn't enough, BW buffed Storm Drain into an immunity to Water-type moves, granting Gastrodon a Special Attack boost whenever it is hit by a Water-type attack. Not much has changed in the transition to BW2, where Gastrodon suffered due to its relative frailness and weakness to status; however, the ban of Genesect and Tornadus-T has breathed life into our beloved sea slug, giving it a place in teams without the constant fear of being obliterated.</p>
<p>Gastrodon can viably be used in rain, sandstorm, and weatherless teams thanks to its attributes, and with its useful ability it comes in handy in the current Water-type plagued metagame. Gastrodon can completely wall common Pokemon such as Starmie and Rotom-W with ease, being immune or resistant to their main attacks. However, not everything is good news for Gastrodon; Celebi, Ferrothorn, and other counters are common in the Overused metagame, and its bulk is not as great as it might seem, making it easy to take advantage of Gastrodon by either easily KOing or setting up on it.</p>
[SET]
name: Defensive
move 1: Earthquake / Earth Power
move 2: Scald / Ice Beam
move 3: Toxic
move 4: Recover
item: Leftovers
ability: Storm Drain
nature: Sassy / Calm
evs: 252 HP / 84 Def / 172 SpD
[SET COMMENTS]
<p>This set enhances Gastrodon's special bulk, allowing for an offensive and defensive presence at the same time. Despite the low Defense investment, the suggested EV spread allows Gastrodon to survive a Close Combat from Choice Band Terrakion and a Choice Band Outrage from Garchomp at full HP. It will also allow Gastrodon to sponge both Psyshock and Secret Sword, taking 56.33-66.43% from Choice Specs Latios and 39.67-47.18% from Choice Scarf Keldeo. While Earth Power benefits from a Storm Drain boost and Gastrodon has a marginally better Special Attack stat, unboosted Gastrodon will usually find Earthquake better to deal with threats with high Special Defense, such as Jirachi and bulky Swords Dance Scizor; however, you should try to burn Scizor with Scald first anyway.</p>
<p>Gastrodon can be used effectively in any kind of team; in sandstorm teams it won't take passive damage, but it shines more in a rain team, as Scald damage is boosted, making it a more perilous threat. Gastrodon can check and counter common offensive threats for both rain and sandstorm teams, being able to absorb all incoming Hydro Pumps, Scalds, Thunderbolts, and Thunders, that would otherwise seriously damage your team members. With its notable special bulk, Gastrodon can withstand anything Starmie throws at it (even the uncommon Grass Knot) and tank a Draco Meteor from Life Orb Latios, forcing it to switch out while Gastrodon heals off the damage. However, Latios will prefer to use Psyshock against Gastrodon. When Gastrodon is in a rain team, Tyranitar has no way of defeating it, and can be crippled by an Earthquake or a possible burn from Scald; however, Choice Band Tyranitar easily 2HKOes Gastrodon. You can use Ice Beam to deal with the many Dragon- and Ground-type threats, as it deals significant damage to Garchomp, Salamence, and Landorus. Still, this will forfeit the burn chance offered by Scald, which, even unreliable, usually makes a better option, as it can be used to to cripple the physical attackers that threaten Gastrodon. Status can be spread easily through Gastrodon's ability to force switches, so Toxic is absolutely required to deal with foes such as Rotom-W and Jellicent, who get walled but don't take much damage from Gastrodon's puny attacks. Recover is not up for discussion; every defensive Gastrodon should use it.</p>
[ADDITIONAL COMMENTS]
<p>You can use a more specially oriented spread of 252 HP / 4 Def / 252 SpD to tank hits from Thundurus-T and Rock Polish Landorus better. An EV spread of 252 HP / 192 Def / 64 SpD with a Bold nature is also viable, and will allow Gastrodon to take physical attacks such as Terrakion's Close Combat. With this spread, Gastrodon has more chances to use Ice Beam effectively, switch into physical attackers, or try to burn Terrakion and Scizor with Scald, as it will be able to take a hit or two from Pokemon with high Attack. Keep in mind, though, that physical attackers locked into one uneffective move will most likely switch out from Gastrodon; also remember that even with maximum Defense, Choice Band Scizor's U-turn still deals a lot of damage. Thus, it's best to use Recover against a Scizor, predicting the aforementioned U-turn to heal back to almost full health after it. Be aware that despite all its traits, Gastrodon isn't really bulky enough to switch into and defeat powerful attackers; to make matters worse, any status will render it useless.</p>
<p>The best teammates for Gastrodon are, ironically, its foes. Grass-types will resist attacks thrown at Gastrodon and potentially answer with a coverage move. Ferrothorn is a good ally, as it can check Grass-types—not even fearing Hidden Power Fire provided rain is up—and set up entry hazards. Latios and Latias can take Grass- and Fighting-type attacks and obliterate the users of these attacks with ease. On rain teams, SubToxic Tentacruel is another good teammate, since it can check Jellicent, though Scizor can make an even better Jellicent counter due to Pursuit. Both of these Pokemon can tank Grass-type attacks as well, making them even better options. Tornadus-I, which is useful on rain teams due to its powerful Hurricane, can handle Fighting- and Grass-types as well.</p>
[SET]
name: Special Attacker
move 1: Surf / Scald
move 2: Earth Power
move 3: Ice Beam
move 4: Hidden Power Grass / Recover
item: Choice Specs / Life Orb
ability: Storm Drain
nature: Modest
evs: 124 HP / 252 SpA / 132 SpD
[SET COMMENTS]
<p>With either Choice Specs or Life Orb, a Storm Drain boost, and possible Drizzle support from an opponent's Politoed or your own, offensive Gastrodon is a very real threat, and is to be feared in today's metagame. With its perfect neutral coverage and acceptable bulk, Gastrodon can power through a wide variety of foes. To put its power into perspective, with all of its potential boosts added together, Gastrodon has the equivalent of 1046 Special Attack when using Surf. Opponents can't simply switch into Gastrodon. In fact, a rain-boosted +1 Surf is a guaranteed 2HKO to physically defensive Ferrothorn. If you predict it switching in, +1 Earth Power deals 52.8%-62.5% to even the most specially defensive variants. +1 Surf under rain also deals 40.49-47.85% damage to standard Blissey; while this unfortunately misses out on a guaranteed 2HKO, it certainly dents Blissey enough to make it scramble for recovery. Hazard support can help here, as with Stealth Rock and Spikes on the field, Blissey will be 2HKOed. Also, in such a case, Choice Specs Gastrodon has a 78.52% chance to 2HKO standard Wish Chansey after Stealth Rock damage. Most opponents will expect defensive Gastrodon; use this to your advantage and surprise unsuspecting foes with a powerful Surf or Earth Power. Ice Beam is a solid choice for coverage and helps in dealing with the common Ground- and Dragon-types threats, such as Dragonite, Garchomp, Landorus, and Salamence. Hidden Power Grass obliterates opposing Gastrodon, and deals with Rotom-W and Politoed. If you are using Choice Specs you could use Recover over Hidden Power Grass on a forced switch, but you will miss out on safely KOing these common Pokemon. A Life Orb set can be used with Recover, but you will fall short of 2HKOing Ferrothorn, and Gastrodon really appreciates the extra power from Specs. However, the ability to switch attacks is a very welcome bonus. Life Orb sets should use a spread of 104 HP / 252 SpA / 152 SpD to minimize Life Orb recoil. Keep in mind when using an offensively oriented Gastrodon that, despite its potential for raw power, it is often outsped and won't be able to tank many hits before fainting.</p>
[ADDITIONAL COMMENTS]
<p>You can use Scald over Surf for the potential burn chance, but it comes with a significant decrease in power. The suggested spread allows Gastrodon to be an offensive presence, dealing heavy damage with Surf or Scald, Earth Power, and Ice Beam, while still being able to take some hits, such as one Draco Meteor from Choice Specs Latios. You can put the Special Defense EVs into Speed to outspeed and 2HKO Chansey 78.52% of the time, given a Storm Drain boost, whilst scoring the 2HKO on Blissey after Stealth Rock and Spikes damage or two switch-ins into just Stealth Rock (these assume rain and a Storm Drain boost). If you're using Life Orb, you should move 20 HP EVs into SpD, using 104 HP / 252 SpA / 20 SpD / 132 Spe to minimize Life Orb recoil. Rain Dance can be run in the fourth moveslot in this case to help with weather wars; however, Hidden Power Grass to deal with Water-types or Recover to heal back the recoil are recommended.</p>
<p>Offensive Gastrodon will appreciate the same kinds of Pokemon that its defensive counterpart likes—mainly teammates that resist Grass and absorb status, as well as Pokemon able to take common powerful attacks such as Close Combat and Outrage. Ferrothorn is the perfect teammate for any Gastrodon, as it can take incoming Toxics, Grass-type attacks, U-turns, and Dragon-type attacks; however, watch out for Scizor's Superpower. Heatran covers Gastrodon's weaknesses perfectly as well and has a good offensive presence at the same time, being able to deal with Dragon-types.</p>
[Other Options]
<p>Most of Gastrodon's other options are outclassed by the moves given. For instance, you'd rather use Toxic over Yawn when inflicting status, as Yawn takes an extra turn and won't work if the opposing Pokemon switches out; it is a decent phazing move, though. Clear Smog is viable in the second slot on the defensive set to stop setup, but its damage will be very low. Memento as a last move can come in handy, forcing a switch when Gastrodon is about to faint anyway; however, Gastrodon is incredibly slow, making it liable to be KOed before it can use Memento. Gastrodon can run Counter and Mirror Coat to deal back huge damage to opponents, but generally the other options will work better, as this strategy is difficult to use and is gimmicky at best. Stockpile is viable, but it is not recommended in the current hyper offensive metagame, as most of the time you will be wasting turns using it or letting opponents set up on you. You could run Hidden Power Fire, but Scald does better against Scizor, and Ferrothorn will OHKO Gastrodon with Power Whip. Additionally, you can use Sand Force in a sandstorm team for a more powerful Earth Power, albeit losing Gastrodon's main niche and one immunity. Sand Force Choice Specs Earth Power will tear apart opposing Steel-types, bar Skarmory and Bronzong. Still, Storm Drain will be a better choice most of the time, since a lot of Gastrodon's effectiveness lies in its use as a rain counter.</p>
[Checks and Counters]
<p>Grass-types are Gastrodon's bane: Venusaur, Breloom, Celebi, Roserade, Amoonguss, Virizon, and Ferrothorn are an immediate switch-out for our sea slug friend. Physical attackers, especially Ferrothorn, must be wary of an incoming Scald, since the burn can ruin them. Ferrothorn will most likely switch-in anyway though, before using Leech Seed on Gastrodon and proceeding to set up all the hazards possible. Most Pokemon with Natural Cure can take a Toxic and switch out, and even take hits from unboosted Gastrodon—Blissey, Chansey, and Shaymin will have no trouble switching into any Gastrodon barring offensive variants in rain. Hydration Vaporeon takes little damage from Gastrodon and will be able to get rid of Toxic. Despite being uncommon, be aware that Politoed and Heatran can use Hidden Power Grass to dismiss Gastrodon in one turn. Fast Substitute and Taunt users will tear Gastrodon into shreds, too—Gyarados, Latias, Jellicent, Substitute + Dragon Dance Dragonite, and Substitute Kyurem get a free switch-in on Gastrodon and a free set up turn. Gastrodon is weak to status itself, so using Toxic on it will cripple its utility, forcing it to switch out before having its HP devoured. In addition to all the previous threats, Gastrodon will have a hard time facing powerful attackers such as Choice Band Dragonite, Terrakion, Kyurem-B, Grass Knot Thundurus-T, Secret Sword Keldeo, Salamence, and Garchomp, even though at full health or with some bulk it can survive a hit from them.</p>
Gastrodon
[Overview]
<p>Gastrodon is a Pokemon blessed in both typing and ability, boasting two immunities, four resistances and a lone 4x weakness to Grass-type attacks. As if that wasn't enough, BW buffed Storm Drain into an immunity to Water-type moves, granting Gastrodon a Special Attack boost whenever it is hit by a Water-type attack. Not much has changed in the transition to BW2, where Gastrodon suffered due to its relative frailness and weakness to status; however, the ban of Genesect and Tornadus-T has breathed life into our beloved sea slug, giving it a place in teams without the constant fear of being obliterated.</p>
<p>Gastrodon can viably be used in rain, sandstorm, and weatherless teams thanks to its attributes, and with its useful ability it comes in handy in the current Water-type plagued metagame. Gastrodon can completely wall common Pokemon such as Starmie and Rotom-W with ease, being immune or resistant to their main attacks. However, not everything is good news for Gastrodon; Celebi, Ferrothorn, and other counters are common in the Overused metagame, and its bulk is not as great as it might seem, making it easy to take advantage of Gastrodon by either easily KOing or setting up on it.</p>
[SET]
name: Defensive
move 1: Earthquake / Earth Power
move 2: Scald / Ice Beam
move 3: Toxic
move 4: Recover
item: Leftovers
ability: Storm Drain
nature: Sassy / Calm
evs: 252 HP / 84 Def / 172 SpD
[SET COMMENTS]
<p>This set enhances Gastrodon's special bulk, allowing for an offensive and defensive presence at the same time. Despite the low Defense investment, the suggested EV spread allows Gastrodon to survive a Close Combat from Choice Band Terrakion and a Choice Band Outrage from Garchomp at full HP. It will also allow Gastrodon to sponge both Psyshock and Secret Sword, taking 56.33-66.43% from Choice Specs Latios and 39.67-47.18% from Choice Scarf Keldeo. While Earth Power benefits from a Storm Drain boost and Gastrodon has a marginally better Special Attack stat, unboosted Gastrodon will usually find Earthquake better to deal with threats with high Special Defense, such as Jirachi and bulky Swords Dance Scizor; however, you should try to burn Scizor with Scald first anyway.</p>
<p>Gastrodon can be used effectively in any kind of team; in sandstorm teams it won't take passive damage, but it shines more in a rain team, as Scald damage is boosted, making it a more perilous threat. Gastrodon can check and counter common offensive threats for both rain and sandstorm teams, being able to absorb all incoming Hydro Pumps, Scalds, Thunderbolts, and Thunders, that would otherwise seriously damage your team members. With its notable special bulk, Gastrodon can withstand anything Starmie throws at it (even the uncommon Grass Knot) and tank a Draco Meteor from Life Orb Latios, forcing it to switch out while Gastrodon heals off the damage. However, Latios will prefer to use Psyshock against Gastrodon. When Gastrodon is in a rain team, Tyranitar has no way of defeating it, and can be crippled by an Earthquake or a possible burn from Scald; however, Choice Band Tyranitar easily 2HKOes Gastrodon. You can use Ice Beam to deal with the many Dragon- and Ground-type threats, as it deals significant damage to Garchomp, Salamence, and Landorus. Still, this will forfeit the burn chance offered by Scald, which, even unreliable, usually makes a better option, as it can be used to to cripple the physical attackers that threaten Gastrodon. Status can be spread easily through Gastrodon's ability to force switches, so Toxic is absolutely required to deal with foes such as Rotom-W and Jellicent, who get walled but don't take much damage from Gastrodon's puny attacks. Recover is not up for discussion; every defensive Gastrodon should use it.</p>
[ADDITIONAL COMMENTS]
<p>You can use a more specially oriented spread of 252 HP / 4 Def / 252 SpD to tank hits from Thundurus-T and Rock Polish Landorus better. An EV spread of 252 HP / 192 Def / 64 SpD with a Bold nature is also viable, and will allow Gastrodon to take physical attacks such as Terrakion's Close Combat. With this spread, Gastrodon has more chances to use Ice Beam effectively, switch into physical attackers, or try to burn Terrakion and Scizor with Scald, as it will be able to take a hit or two from Pokemon with high Attack. Keep in mind, though, that physical attackers locked into one uneffective move will most likely switch out from Gastrodon; also remember that even with maximum Defense, Choice Band Scizor's U-turn still deals a lot of damage. Thus, it's best to use Recover against a Scizor, predicting the aforementioned U-turn to heal back to almost full health after it. Be aware that despite all its traits, Gastrodon isn't really bulky enough to switch into and defeat powerful attackers; to make matters worse, any status will render it useless.</p>
<p>The best teammates for Gastrodon are, ironically, its foes. Grass-types will resist attacks thrown at Gastrodon and potentially answer with a coverage move. Ferrothorn is a good ally, as it can check Grass-types—not even fearing Hidden Power Fire provided rain is up—and set up entry hazards. Latios and Latias can take Grass- and Fighting-type attacks and obliterate the users of these attacks with ease. On rain teams, SubToxic Tentacruel is another good teammate, since it can check Jellicent, though Scizor can make an even better Jellicent counter due to Pursuit. Both of these Pokemon can tank Grass-type attacks as well, making them even better options. Tornadus-I, which is useful on rain teams due to its powerful Hurricane, can handle Fighting- and Grass-types as well.</p>
[SET]
name: Special Attacker
move 1: Surf / Scald
move 2: Earth Power
move 3: Ice Beam
move 4: Hidden Power Grass / Recover
item: Choice Specs / Life Orb
ability: Storm Drain
nature: Modest
evs: 124 HP / 252 SpA / 132 SpD
[SET COMMENTS]
<p>With either Choice Specs or Life Orb, a Storm Drain boost, and possible Drizzle support from an opponent's Politoed or your own, offensive Gastrodon is a very real threat, and is to be feared in today's metagame. With its perfect neutral coverage and acceptable bulk, Gastrodon can power through a wide variety of foes. To put its power into perspective, with all of its potential boosts added together, Gastrodon has the equivalent of 1046 Special Attack when using Surf. Opponents can't simply switch into Gastrodon. In fact, a rain-boosted +1 Surf is a guaranteed 2HKO to physically defensive Ferrothorn. If you predict it switching in, +1 Earth Power deals 52.8%-62.5% to even the most specially defensive variants. +1 Surf under rain also deals 40.49-47.85% damage to standard Blissey; while this unfortunately misses out on a guaranteed 2HKO, it certainly dents Blissey enough to make it scramble for recovery. Hazard support can help here, as with Stealth Rock and Spikes on the field, Blissey will be 2HKOed. Also, in such a case, Choice Specs Gastrodon has a 78.52% chance to 2HKO standard Wish Chansey after Stealth Rock damage. Most opponents will expect defensive Gastrodon; use this to your advantage and surprise unsuspecting foes with a powerful Surf or Earth Power. Ice Beam is a solid choice for coverage and helps in dealing with the common Ground- and Dragon-types threats, such as Dragonite, Garchomp, Landorus, and Salamence. Hidden Power Grass obliterates opposing Gastrodon, and deals with Rotom-W and Politoed. If you are using Choice Specs you could use Recover over Hidden Power Grass on a forced switch, but you will miss out on safely KOing these common Pokemon. A Life Orb set can be used with Recover, but you will fall short of 2HKOing Ferrothorn, and Gastrodon really appreciates the extra power from Specs. However, the ability to switch attacks is a very welcome bonus. Life Orb sets should use a spread of 104 HP / 252 SpA / 152 SpD to minimize Life Orb recoil. Keep in mind when using an offensively oriented Gastrodon that, despite its potential for raw power, it is often outsped and won't be able to tank many hits before fainting.</p>
[ADDITIONAL COMMENTS]
<p>You can use Scald over Surf for the potential burn chance, but it comes with a significant decrease in power. The suggested spread allows Gastrodon to be an offensive presence, dealing heavy damage with Surf or Scald, Earth Power, and Ice Beam, while still being able to take some hits, such as one Draco Meteor from Choice Specs Latios. You can put the Special Defense EVs into Speed to outspeed and 2HKO Chansey 78.52% of the time, given a Storm Drain boost, whilst scoring the 2HKO on Blissey after Stealth Rock and Spikes damage or two switch-ins into just Stealth Rock (these assume rain and a Storm Drain boost). If you're using Life Orb, you should move 20 HP EVs into SpD, using 104 HP / 252 SpA / 20 SpD / 132 Spe to minimize Life Orb recoil. Rain Dance can be run in the fourth moveslot in this case to help with weather wars; however, Hidden Power Grass to deal with Water-types or Recover to heal back the recoil are recommended.</p>
<p>Offensive Gastrodon will appreciate the same kinds of Pokemon that its defensive counterpart likes—mainly teammates that resist Grass and absorb status, as well as Pokemon able to take common powerful attacks such as Close Combat and Outrage. Ferrothorn is the perfect teammate for any Gastrodon, as it can take incoming Toxics, Grass-type attacks, U-turns, and Dragon-type attacks; however, watch out for Scizor's Superpower. Heatran covers Gastrodon's weaknesses perfectly as well and has a good offensive presence at the same time, being able to deal with Dragon-types.</p>
[Other Options]
<p>Most of Gastrodon's other options are outclassed by the moves given. For instance, you'd rather use Toxic over Yawn when inflicting status, as Yawn takes an extra turn and won't work if the opposing Pokemon switches out; it is a decent phazing move, though. Clear Smog is viable in the second slot on the defensive set to stop setup, but its damage will be very low. Memento as a last move can come in handy, forcing a switch when Gastrodon is about to faint anyway; however, Gastrodon is incredibly slow, making it liable to be KOed before it can use Memento. Gastrodon can run Counter and Mirror Coat to deal back huge damage to opponents, but generally the other options will work better, as this strategy is difficult to use and is gimmicky at best. Stockpile is viable, but it is not recommended in the current hyper offensive metagame, as most of the time you will be wasting turns using it or letting opponents set up on you. You could run Hidden Power Fire, but Scald does better against Scizor, and Ferrothorn will OHKO Gastrodon with Power Whip. Additionally, you can use Sand Force in a sandstorm team for a more powerful Earth Power, albeit losing Gastrodon's main niche and one immunity. Sand Force Choice Specs Earth Power will tear apart opposing Steel-types, bar Skarmory and Bronzong. Still, Storm Drain will be a better choice most of the time, since a lot of Gastrodon's effectiveness lies in its use as a rain counter.</p>
[Checks and Counters]
<p>Grass-types are Gastrodon's bane: Venusaur, Breloom, Celebi, Roserade, Amoonguss, Virizon, and Ferrothorn are an immediate switch-out for our sea slug friend. Physical attackers, especially Ferrothorn, must be wary of an incoming Scald, since the burn can ruin them. Ferrothorn will most likely switch-in anyway though, before using Leech Seed on Gastrodon and proceeding to set up all the hazards possible. Most Pokemon with Natural Cure can take a Toxic and switch out, and even take hits from unboosted Gastrodon—Blissey, Chansey, and Shaymin will have no trouble switching into any Gastrodon barring offensive variants in rain. Hydration Vaporeon takes little damage from Gastrodon and will be able to get rid of Toxic. Despite being uncommon, be aware that Politoed and Heatran can use Hidden Power Grass to dismiss Gastrodon in one turn. Fast Substitute and Taunt users will tear Gastrodon into shreds, too—Gyarados, Latias, Jellicent, Substitute + Dragon Dance Dragonite, and Substitute Kyurem get a free switch-in on Gastrodon and a free set up turn. Gastrodon is weak to status itself, so using Toxic on it will cripple its utility, forcing it to switch out before having its HP devoured. In addition to all the previous threats, Gastrodon will have a hard time facing powerful attackers such as Choice Band Dragonite, Terrakion, Kyurem-B, Grass Knot Thundurus-T, Secret Sword Keldeo, Salamence, and Garchomp, even though at full health or with some bulk it can survive a hit from them.</p>