I noticed I suddenly had extra copies of a bunch of legendaries (such as Bloodmage Thalnos, King Krush, Jaraxxus, Al’Akir, …), one card craftable, and the other not. I even tried a deck with the uncraftable Al’Akir copy to see if it’s usable in Wild, and it worked. So I went on and disenchanted the duplicates I could, but I got so much free dust it seems to be too good to be true. I found that 02/09 post about Core/Legacy/Classic/Basic cards, but can’t really make heads or tails of all these things.
In short, do I get to keep those uncraftable legendaries, whose craftable counterparts I disenchanted? And if not, would it be possible to undo my disenchanting of them? I didn’t spend any of the dust I got for them yet, and basically didn’t do anything else ingame.
First, it is possible to “undo” disenchanting right after you disenchant a card. If you leave the disenchanting interface, it is “finalized” and cannot be undone.
Core Set: cards are free for all players (with some rules regarding leveling of heroes), they cannot be disenchanted, they are usable in Standard/Wild/Duels, and most importantly, Blizzard can (and will) remove some of the cards next year, maybe sooner if some balancing comes to their mind.
Classic/Basic as we knew them: moved to the Legacy Set
Legacy Set: Wild/Duels only, most of the cards can drop from Classic packs and/or are craftable.
Classic Cards: a subset of the Legacy Set playable in the Classic format.
I think that the important thing here is that the Core set cards are not owned, but lent. They can disappear, so if a player disenchants a duplicate card from the Legacy set, they can lose access to this card if it is removed from the Core set in the future.
That is how I understand the mentioned post - https://playhearthstone.com/en-us/news/23620129/introducing-the-core-set-and-classic-format I believe. I hope I helped you to understand it better now. If not, feel free to ask more questions.
Ah well, I guess I’ll have to craft them again, should they be removed and I need them in the future. Thank you for your reply!
Yes, exactly. Not sure it is clear enough, so I will add that it is related to Wild/Duels mainly, so re-craft only if needed for these formats next year.
I am missing Edwin in the classic set.
now I open 30+clasic pack and received 2nd copy of King Mukla so duplicate protection doesn’t work 
Did you own it before? I think that if you disenchant a card, it is still counted as “owned” and duplicate rule no longer applies.
Hm, yes.
But it should not work as you describe.
it was common practice after they introduce no duplicate legendaries, to disenchant one and hope you will open it next time “in golden.”
Well, it seems that it worked the way you describe between June 2017 and March 2020. Starting with Ashes of Outland, the behaviour is different.
Source: https://hearthstone.fandom.com/wiki/Card_pack#Duplicate_protection
I am in a similar position as you. I disenchanted my regular King Krush and Golden Cenarius but now I want them back because I heard that we won’t be keeping the new core set.
I issued a support ticket and told them that I didn’t spend any dust at all but they didn’t help me at all.
please let us know when you get a reply
I’m in a similar position. I disenchanted my Golden Bloodmage Thalnos because the UI showed me that I have a golden one from the Core Set. After disenchanting though, I no longer have access to the golden one from the Core Set. Support won’t help me at all and told me to open a thread on the Bug Report forum but I didn’t get a single response.
Blizzard won’t be seeing money from me anymore.