It seems that there is a bug related to the implementation of achievements “Beat Shaman CPU”. I already defeated it on Harrowland, Dueling Grounds, Cavern Survival, Multiplayer Treasure Grove, but I did not get any achievements.
This is a known issue, quoting Nick:
Those achievements happen when you happen to play against the CPU in a simulated multiplayer match, which isn’t guaranteed to happen at any particular time. So yeah, it needs some improvements…
Thanks for answering.
I was confused the opportunity to challenge Shaman CPU directly from here.