Gyarados has had a long and miserable history in the Uber tier, dating way back to DPP. Most people treated it as some sort of joke, and never took it seriously. Not all hope was lost, however, as they were eventually swayed to approve its usefulness. While not awesome, it has a niche in the tier with a support set designed to work under any weather condition, rain and sand in particular. Its somewhat unique typing grants it a Ground and Spikes immunity, as well as resistances to some common attacks such as Fire Blast and Surf. Intimidate is a huge boon to Gyarados's niche in Ubers, as it boosts Gyarados's measly physical Defense stat to levels comparable to that of Lugia's, allowing Gyarados to check numerous physical attackers and act as a wonderful pivot. Unlike most of the weaker walls, such as Giratina and Lugia, Gyarados can do decent damage to things it should be checking, such as Tyranitar, Excadrill, and Ho-Oh. Its base 81 Speed might not seem like much, but it is just enough for Gyarados to outpace most stall-based Pokemon, such as Forretress and Chansey. Access to unique moves such as Taunt, Dragon Tail, Toxic, and Thunder Wave makes it a decent stallbreaker like Heatran; however, Gyarados brings a different list of resistances to the table and checks different threats. Although ever-lasting rain makes Gyarados vulnerable to Thunder, rain boosts the power of Gyarados's STAB attack, while sand teams will appreciate Gyarados' combination of unique typing and Intimidate support to check dangerous sweepers, such as Excadrill and Rock Polish Groudon. Gyarados does have its obvious flaws, however, such as its lack of reliable recovery and weakness to Stealth Rock, which means it cannot take repeated beatings without Wish support.
This set utilizes all of Gyarados's unique attributes as a defensive threat capable of breaking stall and checking dangerous sweepers at the same time. Taunt is its advantage over similar Pokemon such as Giratina and Lugia, as it gives Gyarados the ability to stop the enemy from recovering HP, prevents status moves from being thrown around, and also stops entry hazard users from setting up as long as they are slower than Gyarados. All of the defensive Spikes users besides fast Deoxys-D sets are easily stopped in their tracks by Taunt. Although Ferrothorn can wear down Gyarados through repeated Power Whips, it cannot recover with Leech Seed or set up Spikes. Volt Switch Forretress can be a nuisance as well, and Gyarados also needs to be paired with a Ghost-type, as entry hazards play a huge role in its success. Taunt is also a great move to stop RestTalk users such as Kyogre and Giratina. Thanks to the new sleep mechanics, Gyarados can easily Taunt them on the first turn and phaze them out the following turn, preventing them from doing anything. Thankfully, Gyarados resists Water-type attacks, so mono-attacking Kyogre will not be able to do much damage, although an unlucky burn on the switch will greatly shorten Gyarados's life. Gyarados has good enough defenses to stave off unboosted Dragon Pulses from Giratina and force it out with Dragon Tail. If it tries to recover with Rest, Taunt will just make it useless.
Double switching is important to make proper use of Intimidate, and with the ability in effect, Gyarados can easily live hits from powerful sweepers, such as Rayquaza's Outrage and Ho-Oh's Brave Bird. This unique ability also makes Gyarados a decent team player, and while it cannot support its team in any other way, it is capable of utilizing entry hazards on its own through Dragon Tail—another key move of this set. Gyarados has a usable base 125 Attack to go along with Dragon Tail, and while it lacks STAB, it is powerful enough to deal major damage when combined with entry hazards, especially against the likes of Rayquaza and Kyurem-W. With so many Dragon-types roaming around the tier, Dragon Tail becomes more useful than Roar for Gyarados, and it also wears down common counters such as Zekrom and Palkia. Bulkier threats such as Chansey and Giratina also hate the extra damage they take from Dragon Tail. Waterfall is the most consistent STAB move, and is mainly used to strike common threats it checks, such as Ho-Oh, Excadrill, Blaziken, Genesect, and Tyranitar. Even if the weather is sunny, Gyarados can break Ho-Oh's Substitutes with Waterfall, and cripple the phoenix with Toxic. In rain, Waterfall becomes a decently powerful attack, capable of 3HKOing the likes of Arceus and Chansey. Genesect lacking Thunder will have trouble killing Gyarados, making it an excellent switch-in to the most common Genesect set. Both of Blaziken's sets are walled, and Gyarados can just reply with Waterfall or Dragon Tail it out. Waterfall also comes along with a decent flinch rate, which can come in handy against defensive threats such as Forretress. Earthquake is a good alternative over Waterfall to hit Steel-types such as Dialga and Jirachi. With Earthquake, Gyarados can beat Dialga and Jirachi one-on-one, but will fail if they pack Thunder. Toxic is the best status move to use on this set, as it cripples walls. The combination of Toxic and Taunt can easily take down walls, as they can't heal the residual damage. Thunder Wave is a viable alternative, but Toxic has more use in general and limits the number of times a threat can come in to force out Gyarados.Team Options & Additional Comments >>>
A set with Substitute and Dragon Dance can be used to set up on defensive Pokemon, but it has coverage issues and will either be too slow, or too weak. Roar can be an alternative over Dragon Tail on the first set to phaze out Substitute users, but Taunt already prevents that, and Dragon Tail utilizes Gyarados's good Attack stat. Water + Dragon also happens to have pretty good coverage in Ubers, striking most Dragon-types who resist Water for super effective damage. Substitute can be used on the first set to protect Gyarados from status, but Taunt is generally the better move to stop defensive threats, and Scald isn't that common in Ubers. Gyarados can use other sets, but they are not really effective in the Uber tier. It can also set up on defensive Pokemon such as Ferrothorn and Forretress. A Choice Band set can be used for sheer power while still packing some bulk, but Kabutops is generally better for that thanks to Swift Swim and a powerful secondary STAB move. Rest and Sleep Talk can be used for more recovery, but Gyarados already suffers from 4 moveslot syndrome, and it will be useless when sleeping, especially with the new sleep mechanics. Avalanche can be used to directly OHKO Dragon-types such as Rayquaza, Garchomp, and Salamence, and deal a good amount of damage to Giratina-O, but Dragon Tail is better for phazing. Moxie can be used with Choice Scarf to sweep the opponent, but Gyarados is too slow for that, and Salamence is generally the better choice with its superior Attack and Speed.
Checks and Counters
Any Pokemon that packs an Electric-type move and is bulky enough to take an attack from Gyarados can easily force it out. These threats include Kyogre, Palkia, Dialga, and Zekrom; however, none of them will enjoy taking repeated Dragon Tails combined with entry hazard damage. If they do get in safely though, Gyarados has to switch out or get OHKOed. None of them will enjoy a Toxic to the face either, except Dialga, who hates taking Earthquake, but has good enough Defense to take at least one hit and KO back with Thunder. Zekrom has huge physical Defense so it can survive an Earthquake easily, and Bolt Strike will OHKO, but it does not like taking Dragon Tails on the switch; Kyurem-B can achieve the same thing with Fusion Bolt. Groudon cannot KO Gyarados quickly, but it has huge Defense, and the sun it brings weakens Gyarados's Waterfall. Groudon will not enjoy Toxic, however, and has to be wary of Dragon Tail if it tries to set up Swords Dance. Groudon's Stone Edge fails to OHKO Gyarados, but it can chip off the damage easily due to Gyarados's lack of recovery, assuming Groudon is switching into Gyarados, not the other way round. Mixed attacker Giratina-O resists Waterfall and can take out Gyarados easily with Thunder, or just tear out a chunk of its HP with Draco Meteor.
Ferrothorn can't do much to Gyarados, but it can wear Gyarados down with repeated Power Whips and Iron Barbs, especially when Intimidate is not in effect. If Spikes are up, however, Ferrothorn will not like switching repeatedly on Dragon Tails as it cannot recover with Leech Seed due to Taunt. Darkrai can put Gyarados to sleep with Dark Void and take it out with a boosted Dark Pulse, as long as Darkrai does not come in on Taunt. However, Darkrai does not like taking Waterfalls on the switch, as it will 2HKO. Mewtwo can bypass Intimidate and strike Gyarados hard with Psystrike or fry it with Thunder, however it too will not like switching into Waterfalls in rain. Shaymin-S resists Waterfall and can foil Toxic attempts with a faster Substitute. From there, Shaymin-S can 2HKO Gyarados with Seed Flare. If Terrakion manages to come in safely, its Choice Band set can KO Gyarados. Kabutops can survive one hit and strike back hard with Stone Edge, a guaranteed OHKO with Choice Band. In general, Stealth Rock will hinder Gyarados's ability to switch in freely and repeated hits will bring it down eventually.