Zayle, Shadow Cloak is a neutral legendary minion from the Rise of Shadows set. Golden Zayle is a promotional card from Rise of Shadows' single player content The Dalaran Heist. If you own all five chapters, you receive golden copy of Zayle, Shadow Cloak (among other rewards). As of May 16, 2019, it is possible to craft regular version of Zayle for 1600 dust.
When Zayle is added to your deck, the deck name changes to Zayle's E.V.I.L. Deck and no other cards can be added and any cards added previously will be removed. Zayle will not actually show up during play, you will be playing one of the Zayle's E.V.I.L. decks (list below). If you have a golden copy of Zayle, all cards in your deck, your hero portrait and Hero Power will also be golden; if you have a regular copy, all these will be non-golden, no matter if you own any golden copies of cards in any one deck or not. You can however choose your Card Back, by assigning a favourite Card Back to your Zayle deck.
You will earn experience towards whichever class you played as and wins from Ranked will count towards golden hero portrait for that class.
Zayle, Shadow Cloak is not craftable for New Players until they reach rank 25 and will also not show up in card search until then.