The last puzzle has just been discovered. It is a deck code which starts a puzzle in Wild.
https://www.reddit.com/r/hearthstone/comments/1byubsz/the_final_historys_mysterious_puzzle_entrance_has/
The deckcode:
AAEBAdT8BSiTB/kOjhDSEZAVt2z5rALDtAL2vwLdwgKD1AKM7wKTgAPRiQPEmAOhqQOFsQO6tgOTzQPq4QOR5APy6QOo7wPL+QOmgQSvjgS7rASStQS7zgSX7wSi7wSfpAX9xAWp5QWt6QXa+gXRnAaSngaeogbmqQYAAAEDhM4C/cQF97gD/cQF1JUG/cQFAAA=
However I have encountered a problem with this.
I copied the deck code into my collection and it just refused to trigger the puzzle. It just started a normal game in Wild.
I suspected that the cards which are present in several sets are the problem and I was right.
This card here caused the issue:
You HAVE to use the version from the “Descent of Dragons” set. If you use the core version of this card then the puzzle won’t trigger.
Good luck everyone!