Out of all of the custom Hearthstone cards I've seen, this might be the most likely one to be put into the game in some variation.
Kuja, the Confused was created by daniel_mdf, and it is one Legendary card that I would want in all of my decks. The tilt potential is too real.
Kuja could easily help you take out cards with a lot of health, and little attack, like Ysera. You could even combo with your own cards to take the value to the next level. Blizzard loves to make cards like this. While it likely wouldn't be named the same and look like Kuja, there's probably a Legendary on the way that will share its effect.