http://www.serebii.net/pokedex-bw/648.shtml
[Overview]
<p> In her Aria forme, Meloetta is a moderate threat at best, packing a high Special Attack stat and amazing special bulk fortified by its 100 Base HP. On the downside, she possesses little that her fellow Psychic-types would envy, save for Close Combat, a Ghost immunity, and the ability to transform mid-battle.</p>
<p>“Wait, she can transform?”</p>
<p>Yes, you read that right: transform. While Meloetta may not be all that threatening at first, one successful use of Relic Song transforms her from a beautiful singer into a dangerous dancer, which increases her Speed and Attack stats dramatically, and trades in her STAB on Psychic for STAB on Close Combat. Her Pirouette forme can destroy much of the Dream World metagame with its extremely powerful Close Combat and wide selection of useful coverage moves.</p>
<p>All of these qualities, promising as they may seem, still add up to slightly less than the sum of their parts. Unfortunately, Meloetta is mostly outclassed as an offensive and defensive Psychic-type by the likes of Mew, Reuniclus, and Jirachi. Worse still, she is just as limited by her gimmick as she is enhanced; Relic Song is a weak move and denies her both a useful moveslot and the ability to use Choice items effectively in Pirouette forme. With such limitations hampering her effectiveness, her niche is very small, but nonetheless valuable.</p>
[SET]
name: Mixed Attacker
move 1: Relic Song
move 2: Close Combat
move 3: Thunderbolt / Thunder
move 4: Psychic / Hidden Power Ice
item: Life Orb
nature: Naive
evs: 224 Att / 84 SpA / 200 Spe
[SET COMMENTS]
The apex of Meloetta's potential lies within this set, where the bulky powerhouse traits of her Aria forme and fast offensive nature of her Pirouette forme amalgamate into one oddly effective mixed attacker. The first thing to recognize about Meloetta is that she will always start off in her Aria forme, and thus requires a free turn in order to use Relic Song and transform. The term 'free' is used loosely here, since while Relic Song only amounts to 75 Base Power, Meloetta receives a STAB boost from it, and a 20% chance to put the defending Pokemon to sleep, courtesy of Serene Grace. If given the opportunity, she can transform by finishing off a slower, weakened foe, or one that cannot significantly damage her secondary forme. A timely transformation allows her to easily endure the Dark- and Bug-type attacks aimed at her from the likes of Scizor and Tyranitar. Until then, Psychic suffices as the primary attack of choice for Aria forme, allowing her to check the slower Fighting-types of OU, such as Conkeldurr, Breloom, and Toxicroak.
Once she is in her Pirouette forme, the bulk of her damage will come from Close Combat, Arceus's gift to the Fighting-types of the fourth generation and beyond. Anything left standing after a bout with her will take heavy damage from her coverage moves. Thunder combats Skarmory, Gyarados, and Jellicent in either forme, whereas Hidden Power Ice eliminates Salamence, Dragonite, Gliscor, and Garchomp. Thunderbolt is useful in the event one plans to use Meloetta outside of Rain and the accuracy drop is undesirable, but Pirouette forme will miss the ability to 2HKO Jellicent and OHKO Skarmory after Stealth Rock damage.
[ADDITIONAL COMMENTS]
It is best not to stray too far from the EVs provided, as each point of investment has a specific purpose in mind. 224 EVs in Attack grant Meloetta's Close Combat roughly the same same power as Lucario's in Pirouette forme, and 192 Speed EVs are designed to outpace Tornadus-T after transformation, whereas Aria forme can outspeed up to Adamant Lucario and Jolly Gyarados. The leftover 84 EVs go into Special Attack, giving its Psychic just enough power to OHKO max HP Machamp and Conkeldurr without fail after Stealth Rock damage.
This type of Meloetta is very versatile, can fit on most offensive teams, and performs well against all playstyles. Rainy weather is where it really shines, allowing it to trade in its Thunderbolt for Thunder, an immensly powerful move with a 60% chance of paralysis via Serene Grace. Politoed is highly recommended as a teammate for this set.
Bulky Psychic-types are a problem for Meloetta, as they are not quite 2HKOed by Thunder and can quickly dispatch of its Pirouette forme with Psychic or cripple either forme through status and recovery stall. Scizor is a fine example of a Psychic-type exterminator that works especially well in the Rain – the stormy weather makes Scizor much less susceptible to HP Fire, allowing it to take out an unboosted Celebi or Reuniclus without a hitch. Mew is a little trickier to deal with, since its superb defenses and access to Will-o-Wisp shut down most physical answers to it. Fortunately, Chandelure for a teammate can all but solve any Mew troubles, as it shuts down stallbreaker sets with ease by ignoring Will-o-Wisp, trapping it with Shadow Tag, and KOing with Shadow Ball. Hydreigon can also shrug off Will-o-Wisp and retaliate with Dark Pulse, taking on everything Mew has to offer short of a boosted Aura Sphere or Superpower.
[SET]
name: Stallbreaker
move 1: Hone Claws / Work Up
move 2: Close Combat
move 3: Psychic
move 4: Thunder
item: Life Orb / Expert Belt
nature: Naïve
evs: 252 SpA / 4 Def / 252 Spe
[SET COMMENTS]
Being one of the more unique Pokemon in the game, it would also stand to reason that Meloetta is also one of the few Pokemon capable of using Hone Claws competitively. As the name implies, the primary function of this set is to break stall, using her fantastic offensive movepool to cover every single common member of a stall team in one set. The +1 boost to Accuracy and Attack are useful for Meloetta to utilize both Close Combat and Thunder effectively, giving her a boost on the latter stat to deal major damage to Chansey, Blissey, Heatran and Ferrothorn, while increasing the accuracy of Thunder to acceptable levels without having to change the weather. Thunder allows Meloetta to threaten Politoed, Jellicent, and Skarmory, three integral Pokemon to stall teams, and also allows Meloetta to cripple switch-ins it can only hit for neutral damage, such as Jirachi, Dragonite, and Salamence. Lastly, Psychic is used as Meloetta's sole STAB attack on this set, blowing through the physical walls of stall teams that are not affected by Thunder, such as Hippowdon and Gliscor.
Stallbreaker Meloetta can be used on teams in dire need of a mixed attacker or as a wildcard for defensively-oriented teams to break through their opponents. Meloetta's lack of effective resistances make her more at home on an offensive team, easily switching in and setting up on stall team members such as Tentacruel or Slowbro, provided Scald does not burn. Against offense, Meloetta also makes a surprisingly decent Gengar check, as her Normal-type gives her an immunity to Shadow Ball and her massive Special Defense makes her less susceptible to Focus Blast. When attempting to check Gengar, a Hasty nature is recommended, as a Life Orb Focus Blast can 2HKO Naive Meloetta after Stealth Rock damage, which foils her attempts to check a Gengar under the safety of its sub. In all other situations, a Naive nature is preferred to curb Meloetta's vulnerability to powerful priority attacks, such as Bullet Punch from Scizor or Mach Punch from Breloom.
[ADDITIONAL COMMENTS]
The choice between Life Orb and Expert Belt affects mainly two points of interest: longevity and neutral damage. For example, with Life Orb, a boosted Thunder 3HKOs specially defensive Jirachi (even 2HKOing with one layer of Spikes on the field), while Psychic OHKOs a full health Gliscor. However, with the possible Sand, Hail, or poison damage of a stall team wearing Meloetta down, it could be undesirable to take extra damage from Life Orb recoil. For this reason, Expert Belt is also an option to deal strong super effective damage without wearing down Meloetta's HP. Team members that really appreciate Meloetta's stallbreaking support include Swords Dance Landorus, Terrakion, and Lucario, all of which are troubled against a healthy stall team. If using a Rain team, Virizion also performs well alongside Meloetta, and appreciates her ability to lure and weaken the defensive Psychic-types before going down.
[Other Options]
With moves such as STAB Return, Quick Attack, Stone Edge, Shadow Claw, and U-turn in her arsenal, Meloetta can easily run a purely physical set in her Pirouette forme to some degree of effectiveness, but without any viable boosting moves for sweeping, such as Swords Dance, she will have a much tougher time against physical walls. Calm Mind is a classic boosting option for Psychic-type sweepers and can make its way home on a custom Meloetta set as well, but there are better Pokemon for the job, such as Reuniclus and Jirachi, whose reliable recovery and Toxic immunities allow for prolonged sweeps. Energy Ball and Grass Knot give Meloetta an easier time breaking through the likes of Hippowdon and Quagsire.
[Checks and Counters]
A defensive Psychic-type can throw a monkey wrench in any Meloetta's plans, as her best options for dealing with them are niche options such as Shadow Ball and U-turn. Mew, Celebi, and Jirachi can all avoid the 2HKO from her moves and stall her out with a combination of status, attacks, and recovery. Reuniclus combats her standard mixed attacker set well, but falls to a boosted Thunder from her stallbreaker set. Concerning checks, Choice Scarf users are your best bet, as almost nothing is faster than Meloetta once she has transformed. Scarf Chandelure, one of the most prominent revenge killers in the Dream World metagame, can trap and eliminate a transformed Meloetta with Overheat after suffering a bit of prior damage.
The only viable Ghost-types capable of both halting her transformation and threatening her Aria form are Sableye and Golurk. Once either Pokemon switches into Relic Song, she becomes a sitting duck as Sableye Will-o-Wisps and Golurk deals severe damage with Earthquake. Priority attacks are other alternatives for checking Meloetta post-transformation. Scizor's Bullet Punch and Lucario's Extremespeed can pick her off with relative ease after a Defense drop from Close Combat. An untransformed Meloetta is much more vulnerable, with her lower Speed and Defense leaving her prey to other Dream World powerhouses. Salamence, Landorus, Terrakion, and Genesect all strike fear into Meloetta's Aria form, OHKOing easily with a Choice Band or Life Orb-boosted STAB Attack. Genesect OHKOs with U-turn and the attack boost it receives switching in.