Mulligans
General Mulligans
In general, you want to always keep Fire Fly and Cavern Shinyfinder, as having a turn 1 play and finding Kingsbane are always important. If you have both Shinyfinder and Kingsbane in your hand, you can toss Kingsbane as you'll be tutoring it anyway. Keep Kingsbane only if you don't have Shinyfinder.
Backstab and Miscreant are your two most powerful tools against aggressive decks. When on the coin you should generally keep Edwin VanCleef and ways to make him big: an 8/8 on turn 2 can bail you out of any matchup.
A less aggressive variant of Kingsbane Rogue with an auctioneer package. Fire Fly is actually insane for a couple reasons: 1, there are more aggressive decks in the format so having a 1/2 on turn 1 isn’t bad, and 2. there are some many combo cards in the deck that it’s very useful to have a cheap activator. If you make room for Patches, you can always consider running Swashburglars over Fire Fly if you want.
The bigger flex spots right now are Doomerang, which was always one of the worst performing cards in Kingsbane lists, and the Fan of Knives. Depending on what you face, you can sub out FoK for something else, like Shivs, or even another turn 3 anti-aggro card like SI:7 Agent. Loatheb is potentially cuttable in this meta as well.
Cards to consider are Counterfeit Coins, which help with Auctioneer turns and activating your combo cards, but suck after you play Myra’s, Eviscerate, and 1 or 2 copies of Vanish.