John Gorham Coffin
Digger O'Dell (not part of the achiev)
All 4 of these are within the Defiled crypt.
After trying for several hours i noticed a trend after getting Digger o dell several times and dataminer several times.
Each one was specific to a certain crypt!
I changed my active quest to shattered crown and ran into the chancellors tomb. This way I always started the game inside the tomb and worked backwards. The correct crypt leading to the chancellor only spawned Drury Brown (had him twice) **edit** Now verified to spawn in the real crypt as well is John Gorham Coffin as Kalcory posts below
Digger O dell (lost count after 6+) only spawned in the crypt with no event
The crypt containing the event "jar of souls" only spawned Dataminer (4 times for me)
The crypt containing the event "Matriach Bones" only spawned John Gorham Coffin (once my last ghost needed of the 3)
Maybe it was just a coincidence....If anyone else got something different let me know please.
Hope this helps some people out.