Mulligans
General Mulligans
The high roll is going (any combination of Lightning Blooms / Innervates) + Kael'Thas + Natural Selection as early as possible. But you can also go the route of Keleseth / Shan'do, or at the risk of not being able to utilize the Natural Selection combo later on, you can also go the more standard route of Embiggen Druid.
Kael'thas Sunstrider into Natural Selection enables you to buff literally ALL of your non-destroyed minions as early as turn 3 (2x Lightning Bloom + Kael'thas Sunstrider + Natural Selection). Combine this with the likes of Embiggen, Prince Keleseth and the new Shan'do Wildclaw and an assortment of beasts, and you have a broken AF deck.