Other than one minor visual bug (reported it) the ONLY major complaint is how unfair the final boss is.
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too long; didn't read: Either nerf him, buff the player, allow armour to reduce attacks to 0, give power ups that allow you to bust your enemy by adding attack or allow hand size to be increased again (don't know if it was bad rng or you removed that ability but only got a card that reduced handsize)
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Granted beat the update in one run but had to lose all the lives and beat the boss on the final one. It feels disproportionately more difficult and feels more rng than the previous enemies despite being a card game with luck.
The only major strategy for newer players to give is to only upgrade health and damage but to never die and loss a life until the final boss. Even still, on death you basically redo the level or choose to restart the entire run opposed to continuing the fight with progress saved.
Like one time got a perfect 13 only to be pelted with 15ish damage because the boss got a perfect 15. The only saving grace is when he busts (usually never) or deal the same card attack to make a draw.
Other than that, it is a fine game.