This is the Lyra the Sunshard HS Priest Card from the Journey to Un’Goro expansion due for release in April.
It’s a Priest class legendary minion and the card reads: Whenever you cast a spell, add a random Priest spell to your hand.
You can get Lyra the Sunshard by opening packs from the Journey to Un’Goro set.
*Looks a little underwhelming, it is an Elemental however.