"The first part of catching Spiritomb is to get an Odd Keystone. The easiest way of doing this is to talk to the Blackbelt near the end of Route 208. Once you get it, go to Route 209 and find what appears to be a stone well. Go up to it and place the Keystone into the well.
The second part in your quest for Spiritomb requires Wi-Fi communication with a friend. Go to the Underground and talk to your friend, then leave, come back and talk to your friend again. You have to do this a total of 32 times.
Once that's done, go back to the stone well and you'll be able to fight Spiritomb. It will be at Lv. 25.
The Easy Way: Cynthia's first Pokemon is a Spiritomb. After you beat her, it will be in your Pokedex. That means you can go to the GTS and either ask for a Spiritomb or search for one to trade."
Easier.
The second part in your quest for Spiritomb requires Wi-Fi communication with a friend. Go to the Underground and talk to your friend, then leave, come back and talk to your friend again. You have to do this a total of 32 times.
Once that's done, go back to the stone well and you'll be able to fight Spiritomb. It will be at Lv. 25.
The Easy Way: Cynthia's first Pokemon is a Spiritomb. After you beat her, it will be in your Pokedex. That means you can go to the GTS and either ask for a Spiritomb or search for one to trade."
Easier.