How do you get spirittomb on Pokemon diamond?

To get a spirittomb you will need an odd keystone which you place in the rock pile on route 209.

Then you must go underground and talk to 32 people, not the hikers. You ca nget a friend to go down and talk to you and then go back up and so on for 32 times.

Once you have done that 32 times, you go back to the rock pile on route 209 and you press A on it and you will be battling a lv.20 spirittomb.

Make sure you save it first.