To unlock Morgl the Oracle, you'll have to recruit a friend to Hearthstone and have them reach level 20.
When Blizzard first introduced alternate hero skins for Hearthstone, they came with a hefty $10 price tag. Needless to say, it wasn't particularly well received, and the company has been experimenting with alternate ways of unlocking new heroes. Lady Liadrin, for example, is unlocked by reaching level 20 in World of Warcraft, while Morgl the Oracle, the just-revealed "Murloc Shaman" hero is a reward for recruiting a friend.
Here's how it works: you'll send a friend a referral link, which ties them to your account. Once your friend signs up for an account and reaches a combined hero level of 20, then you will unlock Morgl as a playable hero. As an added incentive, you can also get up to 4 free classic packs by having additional friends hit level 20.
No friends? All your friends already playing Hearthstone? No problem. Hearthpwn has put together a quick guide on how to unlock him the easy way.
The patch also brings with it a handful of bug fixes and visual upgrades, which you can read about here.