Consider banning the use of blue gems on bosses. E.g. with Knight you have 10 (or more) free rounds due to stuns, effectively turning the fight into a no contest.
World boss 2 is a pushover. His most dangerous activity activates only on a flush of 4, which is like 1 in 10 rounds. Otherwise it just sits around healing itself for a paltry 6 HP (on Normal difficulty).
I can see two bugs in the present version: 1) Item upgrades won during expeditions are either not working or not shown on item screen, 2) Arcane Engine is said to increase evocation based on "expedition level" - this is incorrect, the bonus depends on character level in expeditions, not the highest expedition level reached.
Couldn't the game just skip the levels where the enemies cannot damage you due to high armor, and apply XP automatically? It's quite annoying to wait for hours to slog through all those mooks.
This is a nice little game, for a while at least. Then it just becomes boring, with the same enemies and effects all over, and the later levels have 25-30 waves, that's 20 minutes of gameplay. The guards are also quite wimpy against higher-level enemies, only doing reasonable damage at level III or IV, which means you can't protect the knight and horseman adequately.
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Did you put an ace in it? Aces count as 1 or 11 when inserting.