Mulligans
General Mulligans
Prescience is the most important one but the other two are also generally good because they give you access to the right cards for every match-up.
Aggro Mulligans
Lightning Reflexes and Flash of Lightning give you access to board clears in the early to mid game. This mulligan is the same for midrange.
Control Mulligans
These generally help you ramp faster in the combo and control match-ups.
This deck is comparable to Ramp Druid as the most popular combo deck at the moment. What it lacks in comparison in speed and consistency in the direct match-up is made up in terms of board clear and healing capabilities in the aggro match-up. It has great capabilities of multiple successive turns of board clearing for almost no mana due to the combination of Yogg-Saron, Unleashed and Cold Storage. In addition, the versatile discover cards Lightning Reflexes and Azsharan Scroll give you acces to transform cards that help you deal with certain difficult threats.
The combo itself is JIVE, INSECT!, Criminal Lineup and Ring of Tides from Queen Azshara, made possible with a ramped-up Jazz Bass and a free Yogg-Saron, Unleashed that clears your opponent’s board beforehands. However this specific combo is relevant mostly only in control match-ups such as Priest or Warrior and against Ramp Druid where your main goal is to just accumulate your combo pieces as fast as possible. In aggro and midrange match-ups, the best strategy is often to repeatedly clear your opponent’s board and stealing their big minions with Yogg and just using Criminal Lineup on some big minion to overwhelm them in the late game or, even simpler, make them run out of resources with board clears and healing.
I took this deck to climb to legend in 27 matches with a 23-4 record. I did not face any Warlock, Shaman or Demon Hunter decks but for the rest, the hardest match-ups are in my opinion the Druid match-up, because it just ramps faster and the Sif Mage because it can often burn you down from 30 HP before you can finish them yourself.
I chose not to run Inzah because it is just too slow and clunky and it often prevents you from drawing the actually helpful cards with Prescience but if you only face control and combo match-ups, you might consider adding it to achieve your combo one turn quicker. Other possible options are playing with the card ratios of Zap!, Feral Spirit, Lightning Storm and Crash of Thunder depending on your match-ups but I am quite happy with this ratio.