Mulligans
Ramp up to 4 mana as soon as possible, then start utilizing Astral Tiger to its maximum potential.
Combo at 7 and 8 mana. 7 mana or before that use Twig of the World Tree, than round 8 use Medivh, the Guardian to gain 10 mana crystals and use Ultimate Infestation if possible. If you don’t have the combo yet, use twig for Hadronox with Carnivorous Cube to make sure you get the value out of it.
As the games progresses on from round 9, use Hadronox as early as possible. Since you will get it back if it dies with N'Zoth, The Corruptor. So make sure it dies and don’t get Evolve or Polymorph.
In most scenarios, I would prefer using Branching Paths for armour, but it depends on the scenario.
When N'Zoth, The Corruptor is played, you should get back a lot of Astral Tiger together with a Hadronox if lucky.
Control / Mill Druid without Naturalize? … that seems a very strange omission.
It’s not a straight up mill deck, and Naturalize will get removed by Skulking geist