World generation hasn't changed between 1.11 and 1.12.
The only difference between post #1 (OP) and post #3 is that the OP world was created with Large Biomes and post #3 wasn't.
The Mansion doesn't exist close to spawn in the default sized biome world.
Rollback Post to RevisionRollBack
There are no dangerous weapons. There are only dangerous people. R.A. Heinlein
If you aren't part of the solution, then you obviously weren't properly dissolved.