http://www.smogon.com/dp/pokemon/cresselia
I've added the TrickScarf set by Jumpman16. Also the support set evs have been modified due to Garchomps removal. The TrickScarf set has references to Shaymin-S, because I understand that it is not definitely uber yet.
[SET]
Name: Support
Move 1: Reflect
Move 2: Moonlight / Rest
Move 3: Ice Beam
Move 4: Thunder Wave / Charge Beam / Psychic
Item: Leftovers
Nature: Bold
Evs: 252 HP / 252 Def / 6 SpA
[SET COMMENTS]
<p>Reflect and Thunder Wave <repetitive> work well against most of Cresselia's counters. They both help to cut down on damage taken from Pursuit, although Thunder Wave requires a little luck from full paralysis in order to avoid taking a hit. Cresselia works well for countering Salamence, so Ice Beam is the standard attack. The listed EVs allow Cresselia to OHKO minimum HP / SpD Salamence with Ice Beam after Stealth Rock damage, while Salamence only has a small chance to 2HKO with a Life Orb boosted Outrage with Stealth Rock and Leftovers factored in. Charge Beam gives the "Bolt-Beam" combination but is mostly notable for hurting Gyarados in addition to grabbing a Special Attack boost occasionally. Psychic helps to take on Infernape, although paralyzing it with Thunder Wave already makes it much easier for a team mate to finish off.</p>
<p>This is a respectable wall, but Sandstorm cripples Cresselia's Moonlight, leaving it only able to recover 25% per use. Replacing Moonlight with Rest is always an option, but without Sleep Talk you will find Cresselia dead weight on your team when it's sleeping. It is better to pack Aromatherapy or Heal Bell on your team in such a case.</p>
[SET]
Name: Sleep Talk
Move 1: Rest
Move 2: Sleep Talk
Move 3: Ice Beam
Move 4: Charge Beam / Psychic / Thunder Wave
Item: Leftovers
Nature: Calm
Evs: 252 HP / 200 Def / 56 SpD
[SET COMMENTS]
<p>This set is like the above, but Rest / Sleep Talk combination gives Cresselia more survivability, particularly when a Sandstorm dominated environment makes Moonlight undesirable. Once again you have three good options to choose from in the last slot. Charge Beam is going to deter Gyarados again while you're awake, but if you're sleeping, Gyarados will just Taunt you to prevent you from Sleep Talking, and Charge Beam won't do enough to stop Gyarados when Cresselia finally wakes up. Thunder Wave will generally help you more against a lot of other fast sweepers that try to set up on an offensively incapable Pokémon such as Cresselia. Psychic allows Cresselia to deal with Infernape, but quite a significant amount of Special Attack is required to OHKO it. In a Sandstorm and Stealth Rock dominated metagame, however, it is not required to pack a lot of Special Attack, for the indirect damage from Sandstorm and Stealth Rock will aid in destroying Infernape.</p>
[SET]
Name: Calm Mind
Move 1: Calm Mind
Move 2: Psychic
Move 3: Moonlight
Move 4: Charge Beam / Ice Beam / Hidden Power Fighting
Item: Leftovers
Nature: Timid
Evs: 96 HP / 252 SpA / 160 Spe
[SET COMMENTS]
<p>Part sweeper, part tank. This plays somewhat like a Special version of Curse Snorlax. The Speed EVs allow Cresselia to outspeed Adamant Heracross, a major threat to Cresselia (after a Calm Mind, Psychic will OHKO). What you plan on using for your secondary attack depends on your team. Charge Beam is for Gyarados once again, Hidden Power Fighting is for Tyranitar and Weavile, and Ice Beam works on Salamence and Dragonite. Signal Beam is also an option if you want to hit Darks and other Psychic-types. <Signal Beam for Celebi!> However, it does far less damage to Tyranitar and Weavile compared to Hidden Power Fighting and has inferior type coverage. Substitute is an option over Moonlight to avoid status. It should be noted that Cresselia can make 101 HP substitutes which are unbreakable by a single Seismic Toss.</p>
[SET]
name: TrickScarf
move 1: Trick
move 2: Ice Beam
move 3: Moonlight
move 4: Reflect / Psychic
item: Choice Scarf
nature: Bold
evs: 252 HP / 144 Def / 114 Spe
[SET COMMENTS]
<p>Choice Scarf and Trick allow Cresselia to su
rprise so common switch-ins
that expect a weak attack.
<Doesn't make sense. This has no SpA EVs like the support sets, and Scarf doesn't increase Special Attack.> Smart opponents may see the lack of Leftovers recovery on Cresselia and realize that she is running Choice Scarf, so be careful. Ice Beam is the standard attack as Cresselia easily counters most Salamence, being able to come in on any of its moves and threaten a OHKO with Stealth Rock down
<repetitive>. With this set, she is also able to counter Choice Band Salamence, which the standard set cannot do.</p>
<p>When Cresselia is done with its Choice Scarf, it can Trick it onto a Pokemon that could otherwise set up on it, like opposing Calm Mind Cresselia, CurseLax, and Calm Mind Suicune, crippling them for the rest of the match.</p>
<p>Reflect allows Cresselia to protect itself against the Pursuiters that commonly come in on her, such as Choice Band Tyranitar and Heracross. If they are not a problem, feel free to run Psychic over Reflect for the ability to beat more threats. Moonlight can be used before and after Tricking Choice Scarf, as it is helpful to stall out Outrages. Charge Beam is an option in the last moveslot to deter Gyarados from switching in, although it is most notable for providing the "Bolt-Beam" combination as well as offering the chance to increase Special Attack.</p>
<p>The EVs allow Cresselia to outspeed
positive
Speed natured base 110s, most notably Gengar, who she has a very slight chance to KO with Psychic after Stealth Rock damage. However, Gengar is commonly Scarfed and will beat Cresselia with Shadow Ball, especially if Cresselia lacks Psychic.</p>
[Other Options]
<p><not relevant>Cresselia learns Grass Knot and Shadow Ball, although neither is especially inviting when compared to its other options. Hidden Power Fire allows Cresselia to combat any Scizor that dares switch in. Sunny Day makes Moonlight much more effective, and can be used once you have eliminated Tyranitar, Hippowdon, and Abomasnow. It does limit Cresselia's moveset, but is worth considering if you also have a Fire-type to benefit from it. Light Screen can be used over Reflect should your desire some extra protection from special attackers. Recycle is an option over Sleep Talk if you opt to use a Chesto Berry. Psycho Shift could work with a Flame Orb to cripple Tyranitar and Scizor switch-ins. Toxic is a fine choice on something this bulky. You can use Protect in conjunction with Toxic to scout Heracross's Choice Banded or Choice Scarfed moves and switch to an appropriate counter. Additionally, Toxic in tandem with Reflect can whittle down even a Choice Banded Tyranitar.</p>
<p>Special mention goes to Lunar Dance, Cresselia's signature move. If you're willing to sacrifice Cresselia, you can revitalize a stricken teammate with it.</p>
[EVs]
<p>There are a lot of ways to manage EVs on Cresselia. Here are a few EV spreads to consider.</p>
<p>Bold 252 HP / 252 Def / 6 SpA. This guarantees Ice Beam will OHKO a minimum HP / SpD Salamence after Stealth Rock damage and focuses on taking physical hits.</p>
<p>Calm, 252 HP / 200 Def / 56 SpD. This provides Cresselia with optimized defenses, allowing it to take hits from both sides of the attacking spectrum.</p>
<p>Timid, 96 HP / 252 SpA / 160 Spe. This hits 270 Speed, allowing Cresselia to outspeed Adamant Heracross and KO it with Psychic after a Calm Mind.</p>
<p>Generally, you should be focusing on Cresselia's HP and defenses. Speed EVs aren't required unless you're running a Calm Mind or Choice Scarf set.</p>
[Opinion]
<p>Being a primarily defensive Pokémon, Cresselia's lack of a reliable recovery move is somewhat of a let down, compounded by the fact that it is weak to Pursuit and lacks many important resistances (although the Fighting and Ground resistance are welcomed). Still, Cresselia has massive defenses that even Lugia would be proud of and while its attacking power is rather weak, Cresselia's decent movepool allows it to function as a great counter for many of the more potent attacking threats in OU, such as Salamence, Gyarados and Infernape. Cresselia is very tough to take down, making it a solid addition to most OU teams.</p>
[Counters]
<p>Tyranitar, Heracross, Weavile, Scizor, and Houndoom do lots of damage with their STAB Dark and Bug moves, often much more than Cresselia can handle. Metagross is virtually immune to all of Cresselia's attacks. All of them can use Pursuit too, and while Cresselia's durability is enormous, it can be almost knocked out by a Pursuit from Tyranitar or Weavile if it tries to switch out. Thunder Wave and Reflect really help out against a lot of these, however.</p>
<p>Blissey just shrugs off Cresselia's attacks, but a Cresselia vs. Blissey match usually descends into a stall fest unless one of them is carrying Calm Mind or Charge Beam. Rest Cresselia will win in the end, though, while Moonlight Cresselia is easily stalled out of PP if a Sandstorm is active. Snorlax will easily take Cresselia's attacks and can just Curse up and finish Cresselia off with its STAB attack or Crunch. Jirachi can come in and set up Calm Minds against Cresselia as long as it doesn’t switch into a status move. Curse Swampert can come in, only fearing the rare Grass Knot and set up against Cresselia.</p>
<p>Generally, you'll find that Cresselia relies a lot on status, Calm Mind or a super effective move to really stop things that can set up. Without Charge Beam, Dragon Dance + Taunt Gyarados is going to set up on it with ease. Swords Dance or Nasty Plot Infernape can outdamage those Cresselia without Psychic, Thunder Wave or Toxic.</p>