Mulligans
General Mulligans
The three top performing cards for me are Daring Fire-Eater, Stonehill Defender and Arcane Tyrant.
Daring Fire-Eater makes your hero power do extra damage to kill an opposing Stonehill, or to just hit face (4Head). Since we wanna do as much damage with the hero power as we can, this is the best way to do so.
Stonehill Defender makes a body that makes another body. These bodies usually are dummy thicc so we can play them on the board and our opponent will need to either attack into them with smaller dudes or use removal.
Arcane Tyrant is such a tempo swing after using a board clear. One of my favorite plays to do is use a Dragon's Fury, wrath the board for 5 damage, and then instantly put out 10/12 of stats with two Arcane Tyrant and a Fire Fly on turn 7. It's so fun and if you were behind before that play, you just turn the whole match on it's head for 7 mana.
Aggro Mulligans
Aggro is a fairly easy matchup to mulligan against.
Stonehill gives two bodies to defend your face from SMOrcing.
Tar Creeper will force uneven trades from the opponent.
Pyromaniac gives you cards for each HP kill you get, which is what we wanna do anyway.
Blast Wave is good against a opponent that wants to flood the board with small dudes, like Paladin.
Midrange Mulligans
For Midrange, you want cards that can deal with their early and late-game stuff as well.
Daring Fire-Eater can help kill any 4 health minion for 3 mana, and if you pair it with Pyromaniac, you can even draw a card for your troubles.
Stonehill Defender stalls the early game and gives you another taunt for their other threats once it dies.
Voodoo Doll is easily Assassinate for mage and can clear anything, no questions asked, early or late game.
Combo Mulligans
The cards I'd mull for against combo are a little skewed, since I didn't play combo much with this deck. Voodoo doll is fine to keep in your hand until one of their combo pieces hits the field, and since combo tries to play the long game, you probably don't even need to mull for it, but it's fine to have as a panic button.Astromancer, since you're gonna be playing over turn 10, it's good to have something that gives you a benefit for having cards in your hand. Even getting a 5-6 drop off it is usually fine, since it's simply another threat the opponent has to handle before they can combo off.
Stonehill Defender is interchangeable with Tar Creeper, but I'd say it's better with Astromancer in hand, since you essentially draw a card that has taunt, and you can hit The Lich King and other big stuff with it to stall the board out.
Control Mulligans
Control v Control is one of the more fun matchups in my opinion, though there isn't much I'd say to mulligan for. You can make an argument for Voodoo Doll, but you have to make them count, and you don't need them in the early game, so there's no reason to dig for it.
Black Cat is card draw on a 3/3, including spell damage, which doesn't usually apply, but it can in specific circumstances.
Astromancer is always good in the extended matches where you hit those later turns and have a ton of cards in your hand, a turn 7 Astromancer is a threat to deal with that the other control deck will want to use their removal on, protecting your Jan'alai that much more.
This is probably my best win-rate deck that I own for the current standard (03/27/2019, Year of the Raven).
It’s one of the more skill-testing decks I think there is on the tier list. Even though this is definitely not even tier two, it still can put up a fight against tier one with some discipline and thought before you sling cards.