Demonheart is a Warlock spell card (rarity: epic) that belongs to the "Goblins vs. Gnomes" set, which was released on 08.12.2014 and is one of initially 123 cards. The artist of this card was Kerem Beyit, who also made 3 other artworks for Hearthstone.
The card costs 5 mana and its card text reads: "Deal 5 damage to a minion. If it's a friendly Demon, give it +5/+5 instead."
The flavor text of the card is the following: Virtually every member of the pro demon lobby is a warlock. Weird.
Based on 98 quiz answers, the card is moderately hard to memorize: 86% of them were correct. The question on “Card text” is answered correctly most often (100%), the one on “Name” least often (74%). An answer takes 6.7 seconds on average.