I returned to hearthstone only a few days ago so this is new to me. If this has been mentioned before then please show me to the right forum. Thanks.
So I have recently discovered that the core set and classic set count as 2 separate sets now, but I basically have the classic legendaries and yet I can craft them again as they are marked in a different set? I have a King Krush from core set for example, and through checking the classic set I can craft him?!?!
What I am missing to explain this, and if I craft another King Krush (which I won't), will it show me to have 2 different versions of the same legendary card?
Core set card are temporary. Every year they rotate, so once the next rotation happens chances are you won't have that King Krush anymore. Meanwhile Legacy set (old Classic and Basic) card are yours to keep forever.
Also, you can't use Core set cards in Classic mode. So if you wanted to play Hunter in Classic with King Krush, you need to own it. As well if you want to use it in Wild, after it gets rotated out of the Core set next year, you need to own it if you still want to keep using it.