Mulligans
General Mulligans
Typically any card that strengthens your knights should be kept. Since this deck can take a few turns to really get going, Lone Champion is amazing if you can play him early. Especially with cards like Hand of A'dal can really give you a fantastic start. It may also be worth keeping Lothraxion since you could possibly play him turn 4 with Coin.
Aggro Mulligans
If you have Consecration early it can keep the pressure off you a bit if you start with a bad hand. Especially against Hunters and Druids as most of their early minions only have 1-2 health, you can board wipe before they can buff them while giving you time to power your knights. Lone Champion is great as always.