Question

How do you get spiritomb on Pokemon white2?

Answer 1

If you have completed the quest with Yancy/Curtis and their lost Xtransceivers, they will then trade Pokemon with you each day in Nimbasa City. Spiritomb is the Pokemon they'll trade you on the eighth day. You can trade any Pokemon for it, so just give them a Patrat or something else that hasn't much use.

Answer 2

You have to have completed the Yancy/Curtis side quest. This side quest is about the Dropped Item (Xtransciever) you find in Nimbasa City.

This Dropped Item can be found in this location:

('Xcuse the dimness of the picture)

Just read this page for what else you should do.

Hope I helped. :)
Source: Above Link