Introduced in Diamond and Pearl, Spiritomb was a tough Pokemon to obtain if you didn't have a friend who was willing to enter and exit the Underground with you 32 times. Although they don't look anything alike, Spiritomb is like a Sableye 2.0 in a lot of ways, since they have the same typing and similar stats.
Like so many other Pokemon, Spiritomb is also based largely on Japanese folklore. It's said to be formed from 108 spirits, which is the same number of spirits that are banished during a Buddhist New Year tradition in order to ward off temptation.
Training tip: With no weaknesses and solid defense stats, Spiritomb is a respectable defensive Pokemon. With its Pressure ability (opponent uses two PP instead of one each time), it definitely has the ability to wait out its opponents, especially if it has a solid recovery strategy like Rest/Sleep Talk.
Beginning in generation four, a female Snorunt evolves into Froslass when exposed to a Dawn Stone (factoid: she and Gallade are the only two Pokemon who evolve via Dawn Stone). Snorunt and its original evolution, Glalie, are both pure Ice-types, making Froslass the only Ghost-type in her family.
Kimono-clad Froslass may look harmless, but it's said that she freezes her prey with icy cold breath and then displays the bodies in a secret trophy room. Furthering her creepiness, she may be related to the notorious Jynx, since both are dual Ice-type and have a female humanoid appearance.
Training tip: Take advantage of Froslass's super high speed stat and send her out first to get in some quick hits. Powerful Ice Beam is a must, which takes advantage of Froslass's Ice typing and has a chance of freezing the target.
Ghost-type Pokemon usually have a unique angle, and Rotom is no exception. When Rotom was introduced in Diamond and Pearl, it has a single form and was purely Electric/Ghost type. In Platinum, Rotom's five electrical appliance forms were added, but transforming Rotom into different forms didn't affect his typing. In Black and White however, Rotom loses his Ghost typing when it transforms into an appliance, so we'll focus on original Rotom today.
Rotom originally appears in the Old Chateau in D/P/P, a creepy place in its own right. Multiple ghosts inhabit the abandoned mansion, including a little girl who can be seen in a room adjacent to where you're standing, but if you go looking for her she disappears. Reminiscent of the movie Poltergeist, you can only find Rotom if you approach a creepy old TV in the bedroom of the chateau at night.
Training tip: Take advantage of Rotom's great special attack stat – powerful and paralyzing Thunderbolt is a must for original Rotom's moveset. Shadow Ball (TM30) is also a solid Ghost-type option.
The Renegade Pokemon – the only legendary with Ghost-typing (including Black and White), Giratina is a fearsome Pokemon in both its forms. Banished from our dimension for its violence and aggression, this Ghost/Dragon type is the most terrifying member of the dragon trio (Palkia and Dialga being the other two 4th gen dragons).
Despite its ferocity though, it's the only dual-type Pokemon to have a weakness to both of its own types, but it makes up for it with the highest HP of any legendary Pokemon.
Training tip: Choosing between Giratina's Altered forme and its Origin forme (have Giratina hold a Griseous Orb in Platinum) depends on whether you want to focus on offense (Origin) or defense (Altered). Its attack and special attack stats are dead even, so you can keep your opponent guessing by using a mix of both.