Hadronox is a Druid minion card (rarity: legendary) that belongs to the "Knights of the Frozen Throne" set, which was released on 10.08.2017 and is one of initially 135 cards. The artist of this card was Zoltan Boros, who also made 249 other artworks for Hearthstone.
The card costs 9 mana, has 3 attack and 7 health, and its card text reads: "Deathrattle: Summon your Taunt minions that died this game."
The flavor text of the card is the following: The viziers of Azjol-Nerub released Hadronox as a last-ditch effort to hold back the Lich King. They did so by VERY carefully scooping him up in a LARGE newspaper and releasing him.
Based on 133 quiz answers, the card is easy to memorize: 92% of them were correct. The question on “Name” is answered correctly most often (95%), the one on “Attack” least often (83%). An answer takes 5.5 seconds on average. In the Pixel Quiz, which shows only the shape and colour of the card, it was recognised correctly 83% of the time.