Hidden Oasis is a Druid spell card (rarity: rare) that belongs to the "Saviors of Uldum" set, which was released on 06.08.2019 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 6 mana and its card text reads: "Choose One - Summon a 6/6 Ancient with Taunt; or Restore 12 Health."
The flavor text of the card is the following: Amazing that it's been hidden, given the twenty-foot treant splashing around in it.
Based on 88 quiz answers, the card is easy to memorize: 97% of them were correct. The question on “Name” is answered correctly most often (98%), the one on “Cost” least often (95%). An answer takes 8.5 seconds on average. In the Pixel Quiz, which shows only the shape and colour of the card, it was recognised correctly 86% of the time.