Defensive
<h3>Misdreavus</h3>
<img src="/download/sprites/bw/200.png" alt="" />
<p><strong>Typing:</strong> Ghost<br />
<strong>Base Stats:</strong> 60 HP / 60 Atk / 60 Def / 85 SpA / 85 SpD / 85 Spe<br />
<strong>Abilities:</strong> Levitate</p>
Misdreavus is deceptively bulky Ghost-type that can quickly become infuriating to take down. It's a great spinblocker that deal with most of the Rapid Spinners in RU. Misdreavus's has a large support movepool that has attacks like Pain Split, Heal Bell, Will-O-Wisp, Taunt, Thunder Wave, and Perish Song. She isn't a slouch offensively either because she has Calm Mind and Nasty Plot backed by a base 85 Special Attack. Misdreavus has no reliable recovery not even Leftovers, so she will eventually succumb to chip damage. In addition, Dark-types can trap Misdreavus if they can avoid Will-O-Wisp, preying on her lower base 60 Defense.
Offensive
<h3>Spiritomb</h3>
<img src="/download/sprites/bw/442.png" alt="" />
<p><strong>Typing:</strong> Ghost / Dark<br />
<strong>Base Stats:</strong> 50 HP / 92 Atk / 108 Def / 92 SpA / 108 SpD / 35 Spe<br />
<strong>Abilities:</strong> Pressure / Infiltrator</p>
Spiritomb is one of the few Pokemon that don't have any weakness, which is a blessing for any Pokemon. Spiritomb has great defenses that are off-setted by a base 50 HP. Spiritomb is a good spinblocker that can combat common Rapid Spinners such as Kabutops and Cryogonal. The even offensive stats means that Spiritomb can go either physical or special, but a shallow movepool hinders Spiritomb's potential. Spiritomb has an innate ability to trap Psychic- and Ghost-types with the gambit of Sucker Punch, Pursuit, and Crunch. A Choice Band set is common to trap the many Pokemon, not just the aforementioned types. A BlackGlasses set can bluff a Choice Band to surprise the opponent. Defensive Pokemon aren't safe either, because Spiritomb can Trick its Choice Band to cripple most defensive Pokemon. Spiritomb's low Speed and HP means that Spiritomb will always be outsped and can't take too many hits, respectively. Any Pokemon that resists Dark-type attacks can take Spiritomb.
Cresselia can be taken off the list now ^^