With lots of easy ways to level up and increase your stats to ridiculous levels it can be anticlimatic when the strongest enemies in the end are 12-14 and only 10 in the various cards.
It would be interesting to have a truly diabolical board expansion to give really powered up characters a challenge , whether a forest/graveyard/vampire tower etc have end bosses in the 20-25 stat range and regular card enemies in the 10-20 range would be great for some more difficult variety and perhaps even a different way to play to switch things up every once in a while.