Hearthpwn

Hi guys, welcome to a new secret mage deck for the Journey of Un'Goro expansion!

Opening hand (Mulligan):

Now due to the wide range of different deck types currently in the meta right now, it's quite difficult to accurately mulligan your hand to properly counter your opponent. This is why, I'll try to give a more general foundation on what you should look for.

General cards you should look for:

Arcanologist - this card is great to have in your opening hand as it removes secrets from your deck. This is essential as secrets lack impact when drawn, so it's better to have them removed from  your deck which will allow for better cards to be drawn. This mechanic resembles Mysterious Challenger.

Babbling book - Not much to be said, apart from it being a very flexible one drop

Kabal lackey - Many opportunities to play secrets with Kabal lackey in this deck. Albeit this card is not always a certainty to keep in your opening hand. 

Medivh's Valet - I would definitely keep this in your opening hand if you have kabal lackey and/or if you have a secret in your hand. 3 damage 2/3 body for 2 mana is nothing to sneeze at.

The rest are situational. Let's give some examples:

Golakka Crawler - Very good against Rogue and Warrior. As Rogue may be the most common deck right now, you should always keep this card in your opening hand.

(Removed: This card should replace a Glyph if you're versing many Rogue or Pirate warrior.)