This boss is basically a Patron wet dream. Every single card in the deck clears the murlocs he plays every turn. Just mulligan for the Grim Patron because whatever else you get in the mulligan will do the same job of clearing murlocs. Use weapons on the buff murlocs so your aoe can clear the 1 health ones.
Once patrons are on the board, basically nothing the boss can do because you just clear and generate more patrons every turn.
In my opinion, this deck is far better and more consistent than the mage ones because mage clears the board with their aoes but you can't maintain any good board presence and eventually you run out of cards. You never run out of value with this deck because patrons generate infinite value without needing to draw more cards.
Please upvote if you had success with it.