Moves
Jirachi makes for a fantastic mixed attacker with its expansive movepool, resilience to passive damage, and excellent Speed. Iron Head is the only necessary move, as it creates free turns, pressures Tyranitar, and disables more physically frail special walls such as Clefable and Blissey with its 60% flinch chance. The remainder of the set is more flexible, depending on the rest of the team.
Ice Punch and Icy Wind take care of the Flying- and Dragon-types; Ice Punch OHKOes Dragonite and Flygon and 2HKOes Gliscor and offensive Latias. Icy Wind is a fine alternative to put more pressure on more physically bulky Pokemon weak to Ice such as Gliscor. The Speed drop also lets Jirachi hit first with Iron Head and prevents Pokemon such as Agility Empoleon and Dragon Dance Gyarados from setting up on Jirachi with impunity should it lack the necessary coverage. Fire Punch hits Steel-types such as Skarmory, Magnezone, Bronzong, and other Jirachi for super effective damage and allows Jirachi fulfull its defensive niche against Scizor and Lucario, as it OHKOes both after Stealth Rock damage. Should Heatran and Magnezone be a concern, Hidden Power Ground is an another option to 2HKO Heatran and OHKO Magnezone without bulk investment after Stealth Rock. Grass Knot hits Swampert, Quagsire, and Gastrondon very hard, at least 2HKOing them while also pressuring Milotic and Suicune. On the other hand, Thunderbolt and Thunder OHKO Gyarados after Stealth Rock and 2HKO Starmie and Skarmory.
Mixed attacking Jirachi has several other options worth considering. Psychic with Special Attack investment OHKOes Gengar and Breloom and 2HKOes Machamp. It also 3HKOes RestTalk Rotom-A, something Jirachi is unable to achieve with any of its other moves. Hidden Power Fire hits Metagross, physically defensive Skarmory, and Breloom harder than Fire Punch. However, Jirachi loses the option to burn its foes and cannot Speed tie with mixed Flygon and opposing Jirachi due to the 30 Speed IV required for Hidden Power Fire.
Set Details
Mixed attacking Jirachi typically runs close to or maximum Speed EVs to Speed tie with other Jirachi and Flygon then invests in one of its offensive stats. However, Jirachi can also opt to lower its Speed investment to hit harder. Useful Speed benchmarks are 320 Speed to outspeed Modest Latias and Gliscor; 308 Speed to outspeed Lucario and Roserade; 300 Speed to outspeed Suicune, Rotom-A, and neutral-natured Zapdos and Flygon, and 280 Speed to outspeed Adamant Lucario and Heatran. For more specially oriented Jirachi, alternative EV spreads include 4 Atk / 252 SpA / 252 Spe, 36 Atk / 252 SpA / 220 Spe to outspeed Modest Latias, and 116 Atk / 192 SpA / 200 Spe with a Special Attack-boosting nature to OHKO offensive Swampert with Grass Knot and an Expert Belt. While Jirachi can use both Defense- and Special Defense-hindering natures, Naive is more common, as Jirachi simply isn't bulky enough without investment to be a long-term pivot into Latias, and keeping its Defense intact allows it to answer threats such as itself, Gyarados, Tyranitar, Breloom, and Dragonite better. Jirachi has a small chance to be OHKOed by Tyranitar's +1 Fire Punch after Stealth Rock with a Defense-reducing nature.
The most common item Jirachi uses is Shuca Berry, as it lets Jirachi survive Earthquake from various Pokemon such as Dragon Dance Gyarados, Dragon Dance Dragonite, Flygon, Metagross, Hippowdon, and Swampert and hit them hard with the appropriate coverage move. Even with a Defense-reducing nature, these Pokemon will fail to OHKO Jirachi with a boosted Earthquake. Another option is Expert Belt, which notably guarantees special coverage moves, such as Hidden Power Ground and Grass Knot, OHKO targets such as Magnezone and Swampert. Leftovers is common to help feign Jirachi not having special coverage moves such as Grass Knot, Thunderbolt, and Hidden Power Ground and gives it the longevity to survive on more defensive teams as a wincon. Lum Berry allows Jirachi to absorb Breloom's Spore and avoid paralysis from Magnezone and opposing Jirachi. In conjunction with Hidden Power Ground, Occa Berry is a decent item to take Fire-types moves from Heatran and Infernape.
Usage Tips
Jirachi has a lot of flexibility and can be brought in at almost any stage of the game. It can lead and hit most leads in the tier hard, come in mid-game to threaten targets such as Swampert, Skarmory, and Heatran with coverage, or wait until late in the game to revenge kill dangerous Pokemon such as Lucario and clean up weakened foes with its Speed. Despite this, it struggles to fulfill the defensive roles bulkier sets can, as boosted Dragon-type moves such as Latias's Choice Specs Draco Meteor and Dragonite's Outrage will 2HKO it. Once it hits the field, Jirachi is straightforward to play: hit the foe with the appropriate move.
Especially if Jirachi isn't holding Leftovers, different item choices can dictate how it should be played. Items such as Expert Belt and Occa Berry can unexpectedly break open holes earlier in the game, while Lum Berry and Shuca Berry are valuable tools to be held hidden to cover specific situations. Shuca Berry variants in particular are often part of the team's backbone against setup sweepers and should be kept healthy for the later stages of the game. Take advantage of how Jirachi can often bluff coverage attacks in desperate situations: for example, switching into Swords Dance Scizor can represent Jirachi having Fire Punch or Hidden Power Fire even if it doesn't have either and can force Scizor out.
Team Options
Mixed Jirachi most often fits on two types of teams: as a late-game wincon and fail-safe against Swords Dance Lucario for both offensive and stall teams based around Spikes, and as an offensive threat and backup answer to Dragon Dance sweepers on faster teams without Spikes. For both offensive and defensive Spikes-based teams, the most common Spiker is Skarmory. Defensive Skarmory can take on Jirachi's defensive roles such as switching into Latias's Draco Meteor, while offensive Skarmory sets can immediately set up entry hazards to put Jirachi's answers in range of its coverage moves. Jirachi can even heavily weaken or KO Magnezone trying to trap Skarmory. On more offensive teams, Roserade can work as well, but it lacks the reliability of Skarmory. On more offensive Spikes-based teams, common teammates include offensive Swampert, Gengar, Choice Specs Latias, Tyranitar, and offensive or Choice Scarf Rotom-A. All of these Pokemon either provide critical defensive utility, take advantage of Spikes themselves, or help keep Spikes up against spinners such as Starmie, Donphan, and Forretress.
For more defensive Spikes-based teams, mixed Jirachi is common on the big 5 style built around Choice Scarf Tyranitar, Skarmory, defensive Latias, Clefable, and either RestTalk Rotom-A or a Ground-type such as Hippowdon, Quagsire, Gliscor, or Donphan. Jirachi provides a more immediate answer to Skarmory with Thunderbolt instead of burning it with Fire Punch and uses its additional coverage to take on threats such as Swampert and Gliscor. More defensive teammates help make up for Jirachi's lack of bulk—whereas more offensive teams are likely to use Jirachi to take on offensive Water-types such as Calm Mind Suicune, Gyarados, and Starmie, defensive partners such as Latias and Clefable can instead, allowing Jirachi to preserve its health for late in the game. These teammates also help Jirachi against difficult foes such as Rotom-A and Zapdos that Jirachi struggles to beat. Note that using such a frail Jirachi forces these Pokemon into particular sets; for example, Skarmory often should be specially defensive, and Latias often needs to have Roar to make up for Jirachi's shortcomings.
On teams without Spikes, Jirachi plays a more supportive role in checking threats such as Dragonite, Swampert, Gyarados, Lucario, and Gliscor with its Speed, item choice, and coverage. As such, it more likely molds its moveset towards its teammates to cover the holes they may lead to. However, it should be used alongside sturdier checks to Latias and Dragonite such as Metagross. Staples of offensive teams such as mixed or Dragon Dance Dragonite, Gyarados, Azelf, offensive Heatran, Dragon Dance Tyranitar, offensive Empoleon, Swords Dance Lucario, Agility Metagross, and Swords Dance Scizor are all good partners. Dragonite and Dragon Dance Tyranitar appreciate Jirachi heavily weakening Swampert and Hippowdon with Grass Knot; Azelf and Gyarados can potentially spread paralysis for Jirachi to take advantage of with Iron Head; Heatran and Empoleon appreciate backup with Dragon Dance sweepers due to Jirachi's Shuca Berry and Jirachi potentially weakening special walls with Iron Head; and Lucario, Metagross, and Scizor appreciate Jirachi targeting Flying-types such as Gyarados, Zapdos, Gliscor, and Skarmory with super effective coverage. Breloom is another great partner alongside versions without Grass Knot, as it can switch into Ground-types trying to target Jirachi with Earthquake. Gengar is another good option, as it can weaken Heatran so that Jirachi can eventually break through.