There are so many episodes of Doctor Who and only so many cards to make, that planechase gave us a few extra places
Feel free to use Wear Down to destroy two combo pieces from the player in the lead, and gift the card to the player furthest behind, or the one you allied with
Aegar possesses the measured temperament of the frost giants, the combat aptitude of the fire giants, and the elemental prowess of both
Changing the as-fan of rarities (that is, the count of each rarity of card you'd expect to see when you open a booster), introducing more variance in slots, adding in more "outside" cards, all impact how the set plays and thus requires us to change how we build the set
Because both players will be top-decking afterwards, you want to ensure that your deck can set up card advantage engines before going off with Awaken
Mutate decks need creatures to mutate onto and enough protection to keep the stack alive