This is the EK0P Yogg Druid w Arcane Giants he was using to climb the ladder on stream.
Yogg Druid is all over the ladder and there is lots of flexibility around a few of the cards. I think 2 x Arcane Giants can be a little too clunky. If you find you keep getting stuck with two in your hand that’s hard to play, switch one for another Nourish.
General Mulligan Guide for Yogg Druid with Arcane Gaints
You follow the general Druid mulligan strategy of keeping ramp and removal. If you can take the lead in mana it’s going to be easier to overwhelm your opponents.
You can keep Mire Keeper if you’re on the coin and have removal. But Wild Growth is more preferable, and Innervates are an obvious choice.