After being teased in the September 15th Patch Notes that Tyrande Whisperwind was coming.
(Note: Twitch Prime is region-locked, don’t know why)
It was just revealed that in-order to get the new hero and her cardback, player would need to get Twitch Prime which was just a recently released service for twitch (If you have amazon prime, you already have it and just need to link your account here.)
Play as the newest Hearthstone hero, Tyrande Whisperwind, Night Elf Priestess and the high priestess of the goddess Elune.
Hero is redeemed through a code, you get from twitch.