This set allows Omastar to hit incredibly hard without suffering from Life Orb recoil. Although this Omastar cannot switch moves, it can check threats such as Ho-Oh, Extreme Killer Arceus, and Swords Dance Ghost Arceus extremely effectively in rain, as it can OHKO all three of them. Omastar can also accomplish feats such as 2HKOing max HP Arceus-Grass and Arceus-Water after Stealth Rock, and 2HKOing Blissey after Stealth Rock and one layer of Spikes. Hydro Pump is the main move Omastar will use early- to mid-game to ensure that it punishes Ho-Oh switch-ins and secures the OHKOs and 2HKOs that Surf cannot. To demonstrate Hydro Pump's power, the move 2HKOes 48 HP Latias after it switches into Stealth Rock twice. Ice Beam easily 2HKOes Latias, usually 2HKOes Palkia after Stealth Rock, and hits the Giratina formes hard. Surf is recommended on the same set despite its redundant coverage, as it allows Omastar to serve as a somewhat reliable win condition late-game, when the enemy's team has been weakened to the point that Hydro Pump is no longer needed. Surf is still strong enough to OHKO Darkrai and Mewtwo, though prior damage is needed for it to KO Arceus. The last move depends on personal preference. Earth Power smacks Dialga and Tentacruel for good damage and can OHKO offensive Dialga after Stealth Rock. However, Hidden Power Rock guarantees the 2HKO on Palkia after Stealth Rock and allows Omastar to check Ho-Oh in any weather, provided the phoenix does not carry Earthquake.

As there are not many Pokemon with Speed stats between those of Mewtwo and Omastar in the rain, Omastar can often afford to run some HP EVs to take hits from Ho-Oh a little easier. However, do not run more than 40 HP EVs on Omastar, in order to ensure that it will outrun Adamant and Modest Deoxys-A in rain. Alternatively, one can choose to run more Speed on Omastar by utilizing a Timid nature, as doing so allows it to outrun uninvested base 90s even outside of rain. In the rain, Omastar will outspeed neutral-natured Choice Scarf Pokemon with base 90 Speed as well as Naive Deoxys-A. The loss of power is noticeable, though, as Timid Omastar cannot OHKO Arceus after Stealth Rock. Omastar's movepool is pretty barren, but Hidden Power Grass can be used in the fourth moveslot to destroy Gastrodon, which otherwise walls this set, and hit Kyogre and Arceus-Water reliably.

Kyogre is required as a teammate in order to use Omastar in Ubers, as the rain it provides gives a boost to Omastar's Speed and Water-type moves. Though Kyogre and Omastar share checks such as Latias and Ferrothorn, they can easily power through them together. Calm Mind Ghost Arceus is a great teammate for Omastar, being able to spinblock the hazards Omastar needs to secure OHKOs and 2HKOs and set up on Choice Scarf Terrakion as it attempts to revenge kill the fossil with Close Combat. In return, Omastar can revenge kill Darkrai and switch into Ho-Oh, two of the best checks to Arceus-Ghost. Other bulky Calm Mind Arceus formes also appreciate Omastar's ability to beat opposing Arceus and Ho-Oh. Ferrothorn makes a good partner for Omastar as well, despite the fact that it is also weak to Rayquaza and Fighting-type moves. Ferrothorn can easily take on most Choice Scarf users that bother Omastar and proceed to set up Spikes. In return, Omastar destroys Ho-Oh and can easily absorb Fire-type attacks aimed at Ferrothorn. Landorus-T can switch in on Choice Scarf Zekrom and Choice Scarf Terrakion for Omastar. It can also serve as a nice switch-in to Groudon and Tyranitar due to its Ground / Flying typing, Intimidate, and ability to threaten them with a powerful Earthquake. Lastly, specially defensive Arceus-Grass can handle Kyogre and Kingdra, both of which Omastar struggles with.

Though Choice Specs Omastar can fit on all rain teams, it functions especially well on rain stall teams alongside Ferrothorn and Tentacruel. This is because it can severely damage offensive sun teams that include Ho-Oh, which teams with Ferrothorn and Tentacruel usually struggle against. Whenever rain is up, Omastar can come in on Ho-Oh and Swords Dance Arceus formes and spam Hydro Pump, which is very likely to knock out an opposing Pokemon. Unlike with Kabutops, Groudon cannot come in on Omastar, or else it risks taking massive damage. Specially defensive Groudon is easily 2HKOed by Ice Beam and Hydro Pump, while offensive Groudon is cleanly OHKOed. If Groudon is sacrificed to stop Omastar's rampage, the opponent loses the weather war and your chances of winning increase dramatically so long Kyogre is still alive. Due to Omastar's lack of reliable recovery, it cannot come in on Life Orb Ho-Oh more than twice. As a result, physically defensive Giratina-O makes a good partner for Omastar on rain stall teams, as it can take two Brave Birds from Ho-Oh and has a useful immunity to Earthquake.

This set eschews the extra power that Choice Specs brings in favor of the ability to switch moves and utilize either Shell Smash or entry hazards. Hydro Pump is Omastar's best move and deals heavy damage to any Pokemon that doesn't resist it. Hydro Pump no longer OHKOes bulky Extreme Killer Arceus after Stealth Rock, but it still does around 80% on average. Surf can be used over Hydro Pump for its consistency, but the decrease in power is noticeable. Ice Beam is needed to deal solid damage to Giratina, Arceus-Grass, and Latias. Earth Power 2HKOes Dialga and Tentacruel but hits little else, whereas Hidden Power Grass defeats Gastrodon.

Omastar can run Shell Smash to double its Speed and Special Attack in one turn, making it extremely difficult to wall and impossible to revenge kill without priority. With Stealth Rock and one layer of Spikes, the only Pokemon that can take any of Omastar's common moves are specially defensive Arceus-Water, specially defensive Kyogre, Ludicolo, Abomasnow, Chansey, and Jynx. Depending on whether Omastar runs Earth Power or Hidden Power Grass, either Tentacruel or Gastrodon can stop it as well. It is sufficient to say that if Omastar is able to get off a Shell Smash, chances are that it will sweep. The trick is to find an opportunity for Omastar to set up, as Omastar's overall bulk is poor by Ubers standards. Forretress and Leftovers Ho-Oh are examples of Pokemon that Omastar can set up a Shell Smash on. Even with proper team support, Omastar will not always find an opportunity to use Shell Smash, but it can still check Pokemon like Ho-Oh. If Shell Smash is not appealing, Omastar can also utilize entry hazards, as it has access to all three. However, it should only run one type of entry hazard, as it will rarely be able to set more than one layer in a match. Hazards can punish switches nicely if the opponent still has a healthy Omastar check, such as Kyogre. If you already have a Spikes user, Toxic Spikes are preferred. If you don't, though, Spikes are often more helpful; it depends on your team's needs.

On the Shell Smash set, Hydro Pump and Surf can be used together in lieu of an additional coverage move. Although running both moves adds to the list of Pokemon that can combat Omastar after a Shell Smash, Omastar becomes more consistent, as it can choose either the raw power of Hydro Pump or the accuracy of Surf. If you want Omastar to function as an all-out attacker, a set consisting of Hydro Pump, Surf, Ice Beam, and either Earth Power or a Hidden Power is ideal. Hidden Power Rock is another option, as it can 2HKO Palkia after Stealth Rock, but it does not provide much additional coverage.

If Omastar runs Shell Smash, there are teammates available that can help it attain a boost. Dragon Dance Rayquaza can bait Choice Scarf Genesect's Ice Beam, which Omastar can easily set up a Shell Smash on. Mixed Dragon Dance Rayquaza can also break down walls that bother Omastar, such as Ferrothorn, while Omastar can switch into Swords Dance Arceus that try to set up on Rayquaza. Shaymin-S also baits Ice Beam from Choice Scarf Pokemon, as it threatens to flinch teams to death if it is not revenge killed. Bear in mind that Ice Beam is not the only Choice-locked move Omastar can set up on. If the opponent lacks priority moves, Omastar can take an attack such as a Stone Edge from Terrakion or an Outrage from any Choice Scarf-wielding Dragon-type in the tier and proceed to set up. Omastar can set up with ease on any Choice-locked Fire-type moves, although it is unlikely that your opponent will be using them in the rain. Wobbuffet can work well as a partner, as if it Encores the opponent into the right move, Omastar can get a free setup opportunity.

Regardless of whether or not Omastar runs Shell Smash, the same teammates that apply to the Choice Specs set also apply here. Ferrothorn and Omastar only share a weakness to Fighting-type moves and can take care of each other's checks. Bulky Calm Mind Arceus formes such as Arceus-Fighting and Arceus-Grass appreciate Omastar's ability to handle Ho-Oh. In return, they can deal with most of the Choice Scarf users that attempt to revenge kill the shellfish. Timid Life Orb Dialga is an intriguing teammate, as it can deal with the weather setters that Omastar is weak to, and resists Electric- and Grass-type moves. A Ghost-type such as Arceus-Ghost or Giratina can provide a reliable switch-in to Choice Scarf Terrakion.