[Overview]
<p>One might wonder why you would use Blastoise in OU as he doesn't have the greatest stats and seems to be outclassed by some of the other bulky Water-type Pokemon. As for a Rapid Spinner, Starmie greatly outclasses him due to it actually being capable of taking down Rotom-A. However, Blastoise does have one unique niche: it can function as an effective OU anti-lead. However, Blastoise fails to deal heavy damage to both Water- and Grass-type Pokemon, meaning that those Pokemon can easily set up on Blastoise. Starmie also has a more effective role outside of the lead position, as it is capable of outspeeding many opposing Pokemon, something Blastoise fails to do. </p>
 
[SET]
name: OU Lead
move 1: Hydro Pump
move 2: Aqua Jet
move 3: Rapid Spin
move 4: Ice Beam
item: Life Orb / Lum Berry
nature: Modest
evs: 144 HP / 252 SpA / 112 Spe
 
[SET COMMENTS]
<p>Blastoise can make an effective OU lead because of his ability to act as a mesh of two similar leads: Starmie and Empoleon. He combines the Rapid Spinning capabilities of Starmie with the bulk and priority of Empoleon. Hydro Pump hits many leads extremely hard, capable of 2HKOing Metagross, Swampert, Jirachi, Machamp, and many other leads provided he holds a Life Orb(with a Lum Berry? Not likely). Aqua Jet finishes off frail Pokemon who use a Focus Sash like Azelf, Aerodactyl, and Infernape, while Rapid Spin removes Stealth Rock and other entry hazards from opposing leads. Ice Beam rounds out the set with a 100% accurate move that can smash through Gliscor and Dragonite leads.</p>
 
<p>The choice of an item is an important one. Life Orb allows you to 2HKO Metagross, Swampert, Jirachi, and Machamp leads 100% of the time and can also 2HKO Colbur Azelf leads with Hydro Pump + Aqua Jet. It also gives Blastoise more power behind his attacks. However, with Lum Berry leads, Blastoise has a better chance of beating Machamp leads as it can 2HKO with Hydro Pump not counting accuracy 80% of the time, whereas with Life Orb, Blastoise has to hope he does not get hurt by confusion followed by another DynamicPunch. Additionally, Lum Berry lets Blastoise beat Smeargle leads and still acquire close to 80% chance of a 2HKO on the aforementioned Pokemon.</p>
 
[Additional Comments]
<p>A Modest nature along with maximum Special Attack EVs allows Blastoise to hit as hard as possible, while 112 Speed EVs lets you outrun max Speed Jirachi after it Tricks you a Choice Scarf and 2HKO with Hydro Pump.(It's the second sentence in this paragraph, I don't think finally fits) Finally, the remaining EVs go in HP to boost Blastoise's overall bulk. These HP EVs also let Blastoise survive a Thunderbolt from defensive Rotom-A, end up in Torrent range, and KO back with a boosted Hydro Pump. No Attack EVs are needed because Aqua Jet should only be used to finish off frail Pokemon. Hidden Power Electric may be used over Ice Beam to prevent Gyarados from setting up, but then Dragonite has the capability of doing so.</p>
 
<p>Blastoise has problems with Grass-type leads like Roserade and Celebi because they can immediately threaten Blastoise with a STAB Grass-type attack. Therefore, a partner that resists Grass-type moves is helpful. Heatran is a good choice as a partner because he resists Grass-type moves and after the Special Attack drop, neither Hidden Power Ground nor Earth Power will be doing too much to Heatran, while Heatran can retaliate with his choice of a STAB Fire-type move. If Heatran has Roar, he can also deal with Ninjask leads and remove the boosts he passes by phazing the opposing Pokemon. Specially defensive Roserade can also work if it switches into Leaf Storm, as he has Natural Cure to remove Sleep Powder, isn't threatened by Hidden Power Fire or Ice after the Special Attack drop, and can absorb Toxic Spikes. Roserade can also switch into Thunderbolt from opposing Starmie, survive an Ice Beam, and retaliate with his Grass-type move.</p>
 
[Team Options]
<p>Blastoise appreciates something that can switch into Grass-type Pokemon like Roserade and Celebi as (Meh, personal preference. You have a similar sentence in the additional comments)they immediately threaten him. Heatran is a great teammate because he has the bulk and the attacking capabilities to deal heavy damage to both of them with his choice of a Fire-type move. Additionally, Blastoise struggles against bulky Water-type Pokemon like Vaporeon and Suicune. A Grass-type Pokemon like Celebi, Shaymin, or Roserade can effectively check those types of Pokemon. Roserade is a great choice because he can also absorb Toxic Spikes that the opposing team set up and can set up his own entry hazards against the opposing team.</p>
 
<p>Gyarados can be a problem if Blastoise doesn't use Hidden Power Electric. Rotom-A can be helpful in stopping Gyarados because of its ability to outspeed if it uses a Choice Scarf or the ability to tank a Waterfall and strike back with Thunderbolt or Discharge (Most standard Rotom-A uses Discharge) ((This is a 100% false statement, and far from the truth. Percentage of Rotom-H that uses WoW: 45.0%. Percentage of Rotom-H that uses Discharge: 14%. I think we can agree that most defensive sets do not use it, and therefore it should not be mentioned)) Furthermore, Pokemon that set up Calm Minds are problematic for Blastoise, such as Jirachi and Suicune. If Blastoise doesn't use Ice Beam then Dragonite will also be a problem, while Kingdra will be a problem to all Blastoise. Swampert can Roar away Jirachi if it doesn't carry Grass Knot or strike back at it with an Earthquake and can counter with Ice Beam against Dragonite. He can also Roar away opposing Kingdra before they acquire too many Dragon Dances. (You’re essentially adding another Grass-type weakness to your team, but that’s up to the OP’s choice)</p>
 
[Optional Changes]
<p>Blastoise can utilize a Choice Specs set to use his new HGSS move Water Spout (Smogon assumes HGSS came out a long time ago). Backed with STAB and the boost from Choice Specs, anything that doesn't resist it will be severely dented. However, the support required to effectively use it, which composes of a Rapid Spinner to remove entry hazards, a Fire-type Pokemon to scare away Celebi and Shaymin, and a Grass-type Pokemon to scare away bulky Water-type Pokemon like Suicune and Vaporeon, means that it will be difficult to pull off a sweep with it. Should one choose to use it, a Timid nature with max Speed should be used to outrun max Speed Adamant Lucario. If using a Modest nature, 208 Speed EVs are needed to outrun positive Speed natured max Speed Tyranitar. (No Choice Scarf?)</p>
 
<p>Alternatively, Blastoise can run a standard defensive set that utilizes Rapid Spin. However, Blastoise, unlike Starmie, fails to deal heavy damage to Rotom-A, the premier spinblocker in the OU metagame. Blastoise can run Foresight and Rapid Spin to bypass Rotom-A, but this is only a one-time deal as Rotom-A can 2HKO with Thunderbolt. Roar and Yawn can both phaze the opposing Pokemon to remove any boosts, while Toxic can cripple incoming Water-type Pokemon and cripple them.</p>
 
[Counters]
<p>Both Roserade and Celebi can switch into even a Life Orb Ice Beam and eliminate Blastoise with their STAB attacks. Vaporeon and Suicune can both wall hits from Blastoise and utilize either Wish or Calm Mind to stall it. Rotom-A can switch into Blastoise's Rapid Spin and deal heavy damage with Thunderbolt and Discharge, (same reason as the previous) but should be wary of a Torrented Hydro Pump. Blissey will stop Blastoise dead in his tracks and can whittle him down with Toxic or Seismic Toss. Gyarados can also switch in and begin to set up Dragon Dances, which Blastoise can stop only if he uses Hidden Power Electric. Kingdra also doesn't take much damage from Blastoise's hits and can set up Dragon Dances like Gyarados.</p>