To get Spiritomb, go to Solaceon Town and go downwards until you see a well-type looking thing. That is the Hallowed Tower, when you press 'A' on it, it will say:

It's the Hallowed Tower.
It appears to have been built
many years ago.

If it asks you to put in an 'Odd Keystone,' say yes. If you already have done so, go down underground with a friend, and have him/her go into his/her secret base and keep coming out and greet you.

Do this 32 times, go back up to the Hallowed Tower, and you will find Spiritomb. It is level 25, and you DO NOT have to see Spiritomb from the Champion Cynthia, I know becuase I did it. You can also do this with Odd Keystones more than once if your friends give you more. I only know of 2. The one by Hearthome City, there's a Karate guy to the left, beat him and talk to him, and the one below.

Already sold your Odd Keystone? No worries, there's another one. Fly to TwinLeaf Town, go down to the water, surf until you get to the middle, then go all the way left and press 'A' on the crack in between trees. If you're having trouble finding it, use your item radar PokeApp which is PokeApp #7.

Submitted by MegaClank (jonathanoct)