One of the most exciting things around the Hearthstone community is the subreddit called "Custom Hearthstone," where creative fans come to share their card design and to see other people's creations. This kind of activity is quite popular, and even some prominent Hearthstone personalities, like Trump, are doing weekly evaluations of the top voted custom cards in the form of a video series.
Each day a lot of people share their ideas, and so it is not unusual that some of those ideas eventually appear in some of the new sets, which has happened before.
But it's unbelievably rare that someone came up with the exact idea of the card just weeks before the reveal of that card, especially if it's some very unique and niche design, far from something simple, that is easier to match with the official card. On March 3, Reddit user FilTheFalcon posted his idea for a card called Abrakadabra.
As you can see, a lot of people in the comments "screamed" that his idea is OP, unbalanced, too strong, and similar negative remarks. But, as it turns out, Blizzard doesn't seem so, because they've designed the exact same card for this set. With the exact same cost and the same effect, even with the same wording, with only added word being "random" for better clarity (Abrakadabra implies randomness of spells).
Of course, it's only a coincidence, since this set was designed and finished long ago before Abrakadabra was shown, maybe as early as in January. Nonetheless, it's still a fascinating coincidence. If you like custom Hearthstone creations, we advise you to follow the Custom Hearthstone subreddit.