There is actually an infinite combo in this game:
Ferocity + Harvest (+ Empty Mind)
Ferocity has a cost of 0, and draws two cards per enemy, including itself.
Harvest is a 0 cost attack card.
Empty Mind will allow you to clear your deck except for Ferocity & Harvest.

You can achieve this combo almost at game start by choosing Samurai to start with Empty Mind, then milling the mystery shop for Ferocity. After that, the only goal is finding Harvest or the two alternates: Backstab and Combo Finisher.
For weapons, I would recommend a dagger so it doesn't take forever to kill the high health enemies. And a crossbow with knockback to deal with the pustule slingers.