Mulligans
General Mulligans
Try to balance draw and control most turns. Doomsayer + Frost Nova is a very sick combo which works best when your opponent has a full board, so they cannot run rush or charge minions into your doomsayer. Focus mostly on draw and board control along the way. Ancient Mysteries is almost always a keep, great for thinning as well as healing.
Aggro Mulligans
Use 1 mo'arg and the arcane artificer as a body in early game is no problem. Ancient Mysteries is both good for thinning as well as ice block/ice barrier pulls for much needed survival. Sometimes you can drop a doomsayer preemptively, but do not waste them!
Midrange Mulligans
In this matchup try to balance draw and control. Spread healing and freezes out over every 2nd turn. Could be a long and rough matchup.