Mulligans
General Mulligans
Northshire and Power Word allow you to both draw and, when used together, play good defense early on. They’re both super useful, especially drawn early. And Lady in White gets more valuable the earlier you play her, when more minions are in your deck rather than hand. You want to play her on turn 6/5 with the coin if it won’t get you killed.
Aggro Mulligans
Most of thee are cards that allow you to survive an early onslaught and get to turn 7, by whichtime you can start playing your bigger anti-Aggro tools. The only exception is Nightscale Matriarch, which you should only keep if you’ve got a Duskbreaker already. She’s a great turn play against Aggro, unless you’re about to die, because then you can start spawning 3/3s or will be forced to trade a lot of cards.
Control Mulligans
You can be greedy here, since normally they won’t come close to killing you for a very long time. Keep key parts of your combos, along with the cards in the general section.