At first glance, Starmie might appear to be a top-tier threat in VGC 2012 with its high base Speed and large movepool. However, even with a Life Orb or another power-boosting item, its base 100 Special Attack is simply not enough for it to beat the opponent's Pokemon before they can KO Starmie. A Focus Sash somewhat remedies this issue, though, and with the right team support, Starmie can cause huge problems to any team.
This set utilizes Starmie's high Speed, decent Special Attack, and great offensive movepool to deal as much damage as possible before it goes down. Hydro Pump is the most powerful Water-type attack that Starmie can use, and it provides Starmie with great coverage in VGC 2012. Ice Beam and Thunderbolt provide BoltBeam coverage, which is particularly effective against the Grass- and Water-types that resist Hydro Pump. Protect has many uses in doubles, as it can be used to stall out an extra turn of Tailwind or Trick Room, and also keep Focus Sash intact. Focus Sash is strongly recommend on Starmie, as it allows Starmie to almost always use at least two attacks.
Thunder is generally the best option for Starmie if it is being used on a rain team, as it needs all of the power that it can get. However, it should only be considered when paired with a Pokemon that has Rain Dance or a Drizzle Politoed. Blizzard can be useful as hail is reasonably common in VGC 2012, thanks to Abomasnow's Snow Warning, and it hits both opponents for around the same amount as Ice Beam; note though that it is somewhat unreliable outside of hail. Psyshock can be very useful for beating Fighting-types, such as Toxicroak, Virizion, and Hitmontop, and also to hit Blissey, Snorlax, and Ludicolo harder, but Protect will be more effective in most battles.Team Options & Additional Comments >>>
Scald is an alternative to Hydro Pump if you would rather not run the risk of it missing, but the power drop is noticeable. Surf is another alternative to Hydro Pump, but it hits Starmie's teammate and is actually weaker than Scald in double battles. Psychic is an alternative to Psyshock, but it does not get any KOs that Psyshock wouldn't; Psyshock is also generally better because it can greatly damage Pokemon such as Blissey and Snorlax. Hidden Power Fire can be used to damage Abomasnow, Ferrothorn, and Shedinja, but it cannot OHKO variants of Ferrothorn and Abomasnow that invest in HP. If you do decide to use Hidden Power Fire, an alternative EV spread of 248 SpA / 12 SpD / 248 Spe should be used. Hidden Power Grass could be used to inflict more damage against Pokemon such as Rotom-W and Gastrodon, but Starmie fails to OHKO either of them. If you do decide to use Hidden Power Grass, an alternative EV spread of 4 HP / 248 SpA / 4 SpD / 252 Spe should be used.
Starmie can play a more supportive role with moves such as Icy Wind and Thunder Wave, but Pokemon such as Cresselia usually do this job much more effectively as Starmie is relatively frail. Recover is an option to avoid Sucker Punch and restore HP, but it is rarely useful in VGC 2012. If you want some extra power, Starmie can hold a Life Orb or Water Gem, but it appreciates being able to take a hit with its Focus Sash. Other Gems can also be used, but they will often not be as effective. A Colbur Berry enables Starmie to beat Weavile, take a Sucker Punch, and survive for a turn against Tyranitar, but Focus Sash is usually the better option, as it allows Starmie to survive an attack of any type. Finally, Analytic is an alternative to Natural Cure, but with such a high Speed stat, Starmie will almost always be attacking first.
Checks and Counters
The likes of Weavile, Speed Boost Yanmega, Jolteon, and Choice Scarf users such as Rotom and Chandelure can outspeed and KO Starmie, but they have to watch out for Focus Sash variants. Sucker Punch users such as Toxicroak and Hitmontop can damage Starmie before it is able to attack, but they have to watch out for Psyshock. Tyranitar can take a Hydro Pump in the sand, knock Starmie to its sash with Crunch, and let sandstorm finish the job. Starmie has difficulty OHKOing many Pokemon, including Zapdos, so if they are not finished off by Starmie's partner, they can pose a threat to it. Gastrodon and Cresselia can take all of Starmie's attacks with ease, but cannot damage Starmie much in return. Ferrothorn, Abomasnow, and Ludicolo are probably the best counters to Starmie, as they take little damage from Starmie's attacks and can hit it hard with the appropriate Grass-type attack. In addition, Starmie has problems against Trick Room teams in general due to its frailty.