Forbidden Ritual is a rare Warlock spell card that belongs to the "Whispers of the Old Gods" set, which was released on 26.04.2016 and is one of initially 134 cards. The artist of this card was Evgeniy Zagumyennyy, who also made 7 other artworks for Hearthstone.
The flavor text of the card is the following: Actually, C'Thun gives his full support for this ritual.
The card is easy to memorize with 98.2% of correct quiz questions.
