I've been playing this for the last several days. I haven't been keeping track of winrate, but I've been staying in the top 30 and have often been in the top 10 so things haven't been going too poorly at least. Regardless the deck is a lot of fun...
The core of the deck is a powerful draw engine of Whispering Wind, Herald's song, Privilege of Rank, and Unstable/Hurler as additional discard fodder. This engine gives you a lot of ways to sculpt your hand and also provides ample fuel for Kosul Brigade. Between Brigades, Magus+Unstable, and Kothon you have a lot of ways to produce multiple threats at once to take over the game from turn 6 onwards.
There are 6 flex slots, which I have filled with 4 Yetipult, 1 Vision of Austerity, and 1 Rain of Frogs. I've been generally happy with Yetipult as a strong anti-aggro and anti-tokens tool that sometimes beats down or draws 3 cards against control, but it's possible that something else would be better here since the card is quite bad against BSH and HotV. Vision and Rain are both very situational, but one of the nice things about our draw/discard engine is that we can usually just discard such cards to Wind, Song, or Brigade if they aren't good. I could see playing 2 Rains since the card curves nicely into Magus; exactly one Vision feels like the correct number though.