Darkest Hour is a Warlock spell card (rarity: epic) that belongs to the "Rise of Shadows" set, which was released on 09.04.2019 and is one of initially 136 cards. The artist of this card was Slawomir Maniak, who also made 99 other artworks for Hearthstone.
The card costs 6 mana and its card text reads: "Destroy all friendly minions. For each one, summon a random minion from your deck."
The flavor text of the card is the following: It's always darkest just before you find the light switch.
Based on 93 quiz answers, the card is moderately hard to memorize: 87% of them were correct. The question on “Name” is answered correctly most often (94%), the one on “Cost” least often (79%). An answer takes 7.7 seconds on average. In the Pixel Quiz, which shows only the shape and colour of the card, it was recognised correctly 67% of the time.