While Slowbro seems like an odd choice for the OU tier, it can be handy for checking some of the metagame's top threats. When using Slowbro in OU, make sure that it isn't being used in a role where it can be outclassed by Suicune and Vaporeon. Slowbro is a blessing on teams that struggle with Dragon Dance sweepers (excluding Tyranitar), and will see the most use on those teams. With its rock-solid Defense and decent Special Defense, however, it can be used as either a physical wall or a mixed wall. Slowbro does greatly struggle with Scizor, however; Scizor can easily switch in on Slowbro's relatively weak Surf and spam a STAB U-turn. Tyranitar can also be a huge problem for Slowbro, as it can deal hefty damage to it via Crunch. While Slowbro is quite bulky, it will fall to powerful special attacks. Gengar's Shadow Ball and Rotom-A's STAB attacks will deal a hefty hit to Slowbro. Don't let these negative factors discourage you, however, as Slowbro can be a huge asset to a team when used correctly.
Slowbro is usually seen in the UU metagame, but it can also be used very well in the OU environment. It is a perfect counter to Machamp, and can take on other top threats like Dragon Dance Gyarados and Dragonite very well. It also has reliable recovery in the form of Slack Off, which sets it apart from its fellow bulky Water-type Suicune.
Surf gives Slowbro a reliable STAB to work with. In the third slot, the move that you use is entirely up to what Pokemon your team needs Slowbro to check. Ice Beam can OHKO Dragonite after Stealth Rock, while Hidden Power Electric is a guaranteed 2HKO on Gyarados, who struggles to 2HKO in return, even with a +1 Adamant Life Orb Bounce. In the final slot, two moves can be used. Thunder Wave is a nice choice for providing paralysis support for slower sweepers like Bulk Up Machamp. Toxic, on the other hand, is more useful for stall teams, as Toxic Slowbro can stall out many of the OU tier's top physical forces with Slack Off.Team Options & Additional Comments >>>
Choice Specs Slowbro can be a dangerous force in OU, as its STAB combination of Surf + Psychic gives great type coverage. An advantage of using Choice Specs Slowbro is that your opponent will never see it coming; Slowbro is uncommon to begin with, and Choice Specs Slowbro is even more so. Slowbro can hit extremely hard with Choice Specs equipped, and as such, should not be underestimated. The great thing about Specs Slowbro is that it defeats its own counters. Scizor and Tyranitar are unable to switch in on a Choice Specs boosted Surf, and Celebi will take huge damage from Fire Blast. More frail Pokemon will have a hard time trying to deal with this Slowbro variant thanks to its amalgam of bulk and power, while defensive Pokemon are crippled with Trick.
Surf is easily Slowbro's best form of STAB, providing nice neutral coverage; Water is a fantastic offensive typing in the OU tier, as the only Pokemon commonly found there that resist it are other bulky Water-type Pokemon such as Gyarados and Vaporeon, Dragon-type Pokemon such as Dragonite, and Grass-type Pokemon such as Celebi and Roserade. Psychic gives Slowbro a nice way of hitting opposing Water-type Pokemon harder than with Surf. Trick is great on Slowbro, as it allows it to cripple any defensive Pokemon, like Blissey, that may be switching in on it attempting to wall its attacks. In the final slot, there are two viable options. Fire Blast is the better choice as it allows Slowbro to handle Steel-type Pokemon who attempt to switch in on it, as well as Celebi. Ice Beam can also be used to get past Celebi. Slack Off is a viable alternative if your team already has a powerful user of Fire-type moves, however, such as Life Orb Heatran.Team Options & Additional Comments >>>
All of Slowbro's more effective options for use in the OU environment have already been discussed. Psychic can be used to hit Machamp harder, but even with a STAB boost and factoring in the super effective hit, Slowbro can still only 2HKO standard 252 HP / 0 SpD Machamp. Slowbro does have access to Light Screen, which can be useful in certain situations if you are aiming for Slowbro to perform more of a support role on your team. It is generally outclassed by Bronzong and Cresselia, however, as far as setting up Light Screen goes. Slowbro can also use Grass Knot as a more powerful means of hitting fellow Water-type Pokemon than Hidden Power Electric, but Slowbro generally has more productive things to do with its precious moveslots. Slowbro also has access to Flamethrower and Fire Blast. While these moves can be useful for hitting Scizor switch-ins for an OHKO, they warrant little use outside of that. Scizor can outspeed and deal ridiculous damage to Slowbro with a STAB-boosted Choice Band U-turn as it is, so Flamethrower and Fire Blast are really only useful if you are positive your opponent is switching in Scizor. Should it not be the metal bug, your opponent will have gotten a new Pokemon in practically for free, while Slowbro will have wasted one of its moveslots.
Calm Mind Slowbro can also be used effectively in OU after Scizor and Tyranitar are taken out by teammates. Calm Mind Slowbro is somewhat outclassed by Suicune, but the fact that Slowbro is much more physically bulky and has two powerful STAB attacks to work with does somewhat help its case. Slowbro is also a great user of Trick Room, as it is one of the slowest Pokemon in the entire game. A simple 252 HP / 252 SpA spread can work wonders on a Trick Room team, as Slowbro's dual STAB combination and decent Special Attack stat can tear through weakened teams. Slowbro is a great support Pokemon in general, and while other Pokemon may have a wider movepool, Slowbro's bulk and access to Slack Off allow it to fulfill a valuable niche on almost any kind of team; moves like Trick, Yawn, and Counter set Slowbro apart from fellow bulky Water-type Pokemon like Vaporeon and Suicune. This is important, as when you are playing with Slowbro in OU, you should try and make sure you're using it in a role where it cannot be "outclassed".
A simple 252 HP / 252 Def EV spread will generally be best, as it maximizes Slowbro's physical bulk; OU is a tier crammed with powerful physical sweepers, and Slowbro needs all of the bulk that it can muster to stand up to these giants. Maximum defense allows Slowbro to survive a +1 Dragon Dance Dragonite's Life Orb Outrage after Stealth Rock damage (to give you an idea of how bulky it truly is). On the Choice Specs set, an EV spread of 252 HP / 252 SpA will generally be the best, as it allows Slowbro to balance bulk and power. It will not be able to take as many hits as it would with 252 EVs in Defense, however; while it is by no means frail when lacking defense EVs, it isn't as bulky as it was, and can no longer survive a Swords Dance Lucario's +2 Life Orb Crunch (among other attacks).
Checks and Counters
As mentioned a few times in the analysis, Tyranitar and Scizor are very problematic for Slowbro to handle. Slowbro, while very bulky, simply cannot stand up to repeated Crunches and U-turns from these Pokemon. Basically, any Pursuit user will give Slowbro a rough time, as they can scare Slowbro away with their STAB attacks and proceed to take out the fleeing Slowbro with Pursuit. Weavile is a major pain for the Choice Specs set, as it can switch in on an expected Psychic and simply Pursuit away as Slowbro has no choice but to switch. Weavile can switch in on Slowbro, but it will lose a large chunk of health in the process due to its frailness and Stealth Rock weakness. Blissey can put a full stop to Slowbro's plans with ease thanks to her absurd Special Defense and HP stats, but she will not enjoy being hit with Trick from the Choice Specs set. Slowbro, as bulky as it is, will not be able to take multiple neutral hits. Slowbro's typing somewhat limits its defensive capabilities, as it leaves it weak to Grass-, Dark-, Bug-, Electric-, and Ghost-type attacks. These attacking types are relatively common in the OU tier, and the fact that most Grass-, Ghost-, and Electric-type attacks are special attacks doesn't help at all. Gengar and Jolteon are big pains for Slowbro, as while they cannot switch in on it, they can certainly come in after a teammate faints; from there, they simply have to spam their STAB move for a clean OHKO on Slowbro.