Really cool game, but the last boss feels unfairly unbalanced, even if you get an amazing deck, just one wrong roll and you lose. If I play like 20 times I'll eventually beat it, but it's so relying on RNG that's not even fun or worth the grind, it's a matter of just getting lucky. Maybe the max for the boss should be 14, or get me an upgrade to get to max 14 (I don't think there is, is there?)
Other than that, great game, I wish it had more balanced content like more paths to explore, more buffs/debuffs, more enemies but with a more balanced math.
The only strategy that works for me is a rerolling based deck and hope to get all perfects to beat the last boss. Every upgrade I choose rerolls (if there's no reroll then I choose heal) and the strat is to stay at or below 7 and reroll for 13