It's hard and you'l need a friend's help. Go to the pillar of rocks (not the Pokemon graveyard) in the route that's in the south of solaceon town (probably route 209) and use explorer kit. Talk to your friend then go up. Repeat it 32 times and spiritomb will appear next to that pillar. Believe me it works. I tried it myself and it worked.However both you and your friend needs to be patient.
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to catch a spiritomb Notice: all the Pokemon in your party have to be at least a lv.70
In the Pokemon Diamond and Pearl games, Spiritomb can be obtained either through the quest in which the player must have 32 interactions with friends, or through the Global Trade Station. If Spiritomb has been encountered by the player, such as through battling the Elite Four and then the Champion, then it can be requested in the GTS system for trade.
Spiritomb
Spiritomb's only weakness in Diamond/Pearl/Platinum is Fighting -- but the only way a Fighting move can hit is if your opponent used a move like Foresight/Odor Sleuth/etc. to enable them to hit Spiritomb with that kind of attack.Otherwise, Spiritomb has NO weaknesses.Spiritomb is a ghost type, which is weak against ghost and dark type attacks.
The Sinnoh League Champion "Cynthia" has a Spiritomb.