Mulligans
Aggro Mulligans
Dirty rat can be risky against aggro decks with big minions (Druid Hydra, Hunter Highmane)
MCTech is great against aggro druid
Control Mulligans
Doomsayer on turn 3 before your twilight drake or mountain giant is very powerful.
In a slow matchup, you can keep faceless if you already have twilight drake or moutain giant if you have a read that they don't have removal.
N’Zoth Renolock in Wild
Leeroy/PO/Faceless combo
Brann/Dirty Rat/MCTech combo
Sludge Belcher/Mistress of Mixtures/Deathlord for the N’Zoth heal/taunt