Fun little game.
This had a lot more frontloaded complexity than I was expecting for a game called "Solitaire Battle". I don't know if that's necessarily bad, but it did stand out to me. Even with it it's a bit visually busy and the animations don't show what's happening as well as they could. For instance, damage indicator text on damage would be nice, or free turns not looking completely indistinct. Passive, active, turn end, etc. skills could have different borders or something.
The shop should unlock automatically when it's empty
I beat the lich with the samurai. Hopefully there's content planned beyond that because otherwise the requirements to unlock the other characters are excessive.