Moves
Surf provides Tentacruel with a reliable attack to check threats weak to Water, such as Gliscor, Heatran, Infernape, Nidoqueen, and Hippowdon. Despite Tentacruel's mediocre Special Attack, Surf 2HKOes Infernape and offensive Heatran, and it can even OHKO Naive Infernape. It 3HKOes most variants of Hippowdon, 2HKOes the physically defensive versions, and 2HKOes most variants of Nidoqueen. Toxic Spikes is the most common third move, as Tentacruel is one of the few Pokemon with access to it. It helps to cripple grounded offensive and defensive Pokemon alike such as Tyranitar, Swampert, Quagsire, and Hippowdon. Sludge Bomb helps overcome Tentacruel's passivity against Breloom, OHKOing it, and can spread status to Toxic Spikes-immune Pokemon like Latias, Gyarados, and Dragonite. Knock Off is another fantastic choice to make up for Tentacruel's general passivity; it can be critical to wearing down defensive Pokemon by removing Leftovers, as well as crippling Choice item attackers trying to exploit Tentacruel such as Flygon, Gyarados, Swampert, and Tyranitar. Knock Off also has excellent synergy with Toxic Spikes, preventing Leftovers from reducing poison damage.
Set Details
Black Sludge gives Tentacruel passive recovery and offsets sand chip damage. Unlike Leftovers, it also dissuades Trick users such as Rotom-A, Metagross, and Latias. The given EV spread and nature let Tentacruel avoid the 2HKO from offensive Timid Heatran's Earth Power after Stealth Rock. The remaining EVs are dumped into Defense to make up for Tentacruel's low Defense stat, letting it better take physical Fighting-type attacks. Alternatively, a Bold nature with a spread of 252 HP / 224 Def / 32 Spe could be used to improve Tentacruel's ability to switch in on physical attacks, as its Special Defense is already quite good. Here, 32 Speed EVs allow Tentacruel to outrun maximum Speed Tyranitar.
Usage Tips
Tentacruel's unique palette of resistances allows it to switch into common Water-, Fire-, Ice-, and Fighting-type attacks effectively, especially from Choice item attackers such as Choice Specs Latias locked into Surf, Choice Scarf Tyranitar using Pursuit or Superpower, and Choice Specs Zapdos using Heat Wave or Hidden Power Ice. Tentacruel preys on bulky Water-types bar Swampert, Fire-types such as Heatran and Infernape, and bulky walls that can't status it, such as Skarmory, some Blissey, and some defensive Jirachi. It uses these Pokemon to remove entry hazards, set up Toxic Spikes, and hit more foes with Knock Off. However, Tentacruel is vulnerable to all entry hazards and sand; therefore, it can't be switching around too cavalierly to remove entry hazards, lest it be too weakened and overwhelmed. This weakness is exacerbated by its lack of recovery. Tentacruel typically enjoys switching in early to establish Toxic Spikes and spread Knock Off, as well as checking threats while it is healthy, and then coming in conservatively afterwards to maintain health for an emergency Rapid Spin. This emergency Rapid Spin is especially effective against defensive teams that lack Rotom-A, as many of their members are passive and don't damage Tentacruel outside of entry hazards. It can even use Toxic Spikes or Rapid Spin against Clefable in a pinch. However, keeping it in against Clefable means Tentacruel risks getting hit by Knock Off or Thunder Wave, the former of which is particularly debilitating. Generally, with its physical frailty and tendency to get worn down, using other Pokemon to get Tentacruel in is advised.
Team Options
Tentacruel fits best on specific teams that benefit from the specific set of roles that it compresses. Though it is an equally rare sight in the tier, Abomasnow absolutely loves having Tentacruel as a partner. It appreciates Tentacruel resisting Fighting and Fire alongside clearing Toxic Spikes and Stealth Rock. In turn, Abomasnow can switch in on Ground-type attacks, and it easily scares out Ground-types like Gliscor and Flygon that threaten Tentacruel. The duo of Tentacruel and Abomasnow is great against most Water-types, with the exception of Gyarados. Hippowdon is another great partner, as it loves having Toxic Spikes cleared, and it appreciates Toxic Spikes being laid down to give it an easier time stalling out the opposition. Magnezone can remove Skarmory and Forretress early on to limit the number of times Tentacruel needs to remove Spikes. Latias and Zapdos can switch in on Ground-type attacks and force out the likes of Gliscor and Flygon, and their best checks being vulnerable to poison, combined with their own instant recovery, lets them take great advantage of Toxic Spikes. Substitute + Roost Zapdos particularly has synergy with Toxic Spikes, potentially stalling out Pokemon like Tyranitar, Swampert, and Hippowdon that would otherwise check Zapdos. Both Pokemon's reliable recovery also makes them reliable answers to Fighting-type and, in Latias's case, Fire-type attacks, making sure Tentacruel isn't overburdened and letting it focus on managing entry hazards. Specially defensive Jirachi ensures Tentacruel won't be overwhelmed by special attackers while being effective with Toxic Spikes due to Iron Head flinching and Wish stalling. Clefable greatly appreciates Toxic Spikes wearing down would-be checks and making it easier to stall out said Pokemon. Tentacruel can also lure in opposing Clefable and cripple it with Knock Off, meaning that Clefable can potentially drop Knock Off itself and use another support move, such as Encore, Thunder Wave, Stealth Rock, or even Heal Bell. The reverse also can be done, with Clefable running Knock Off so Tentacruel can run Sludge Bomb or Ice Beam instead. Calm Mind Clefable, as well as other special attackers, especially likes Toxic Spikes, as it cripples special tanks and walls like Tyranitar, Blissey, and Swampert.
Tentacruel also can be useful for many grounded walls that enjoy Toxic Spikes support. Blissey appreciates Tentacruel's Rapid Spin, as one of Blissey's primary faults as a wall is its vulnerability to all entry hazards, especially Spikes. Blissey can in turn use Wish to heal up Tentacruel, thus mitigating Tentacruel's proclivity to getting worn down. Similarly, Celebi appreciates entry hazard removal alongside Tentacruel switching into special Fire- and Ice-type attacks; Celebi and Tentacruel work well together against almost all Water-types as well. As a fellow Grass-type, Breloom also appreciates Tentacruel's resistance palette and enjoys Rapid Spin support, and in turn, Breloom can break through Pokemon like Blissey, Clefable, Hippowdon, Tyranitar, and Swampert that can wear down or flat out KO Tentacruel. Swords Dance Breloom is especially good at wallbreaking for Tentacruel, as passive Pokemon and Ground-types give it easy setup chances. Though an uncommon sight, Lunar Dance Cresselia also makes for a good partner to Tentacruel, as it can heal Tentacruel of status and bring it back to full health in a pinch; it can also switch in on Ground-type attacks and paralyze Pokemon like Jirachi, Latias, Heatran, Lucario, and Infernape to make it easier for Tentacruel to stay in on said Pokemon.