It's almost always worth mulling for some sort of turn 2 play. Golem or Teacher are ideal, especially if they can attack into a turn 3 onslaught unit (Slagmite, pyromage, or even granite coin can do work here). Generally you should never play power first if you expect to onslaught a pyromage. You want to be able to play the bonus power drawn rather than be forced to discard it.
Heretic's Cannon can steal games by surprise. If the opponent is below 15 health, they're within striking distance of a cannoned heart, groundbreaker, or anything else with double damage or +attack from zuberi. Just be very wary of Icebolt if you cannon your Zuberi (heart, sandstorm titan, and groundbreaker should be safe at 8 health). Also worth worrying about annihilate, or defiance (on a non-sandstorm titan unit). Sometimes it's correct to just go for it, but if you can wait another turn or two for the opponent to potentially tap out, it's something to consider.
Baby Vara can be a real issue if you don't have something to sac to her, or if you don't have Groundbreaker handy.
Slagmite has been great, and the 3/1 body plays into the gameplan of softening your opponent up, and finishing with Heretic's Cannon.
Furnace Mage was added mostly to deal with all the Svetya's Sanctum and Martyr's Chains around, but may not be necessary anymore. They're still useful for clearing permafrost or weights, and the aggressive 4/3 body plays well in this deck.