Turns out I didn’t own any copies, and I just needed to click on the Crafting button.
EDIT:
I was misled because I expected it to show the “You don’t have this card. Check it out in crafting?” prompt, therefore I assumed the card was banned.
Apparently it only shows that prompt when your search exactly matches one of the words in the card title – and I had searched for “biggen” instead of “embiggen”.
But the Devs themselves imply it. It only needs 1 win and then any reward is almost gone or at least it’s poor investment of time for rewards (achievements and some XP).
If they considered it something aimed to be balanced they’d at least need 3 kills.