I've been thinking about shutting this down, but I haven't yet.
Thank you for making it work on my phone. Love that.
Number one, the tutorial needs some work. This isn't any idea or concept, but just advice about tutorials. You packed a lot of information in there and it's nice how detailed it is, but I think it would be better to allow players to skip it all and get to the game if they want to try. A lot of us know how discarding cards works already from other games.
Consider this. Put all the text in a menu that gives information about the game. Allow players to goof around with only the three card deck and then make a few other random stages for the tutorial. Each one introduces a basic concept that needs to be mastered before you can progress. Things like getting the full stats of an item by hovering over it (or as I learned on my own, long pressing the card). Give them multiple cards that all look mostly or even actually the same, but have important information hidden in the full description. Have the game punish them with a tutorial pop-up only if they fail to get the right card.
If the player is really lost and confused, they will have the text in the menu to fall back on.
Number two, right now my first impression is to wonder why I'm playing a old game (I understand it's under active development, but I wouldn't have know that if you didn't link me to it). It looks like it's from 25 years ago and this isn't addressed in the game from what I've seen or even in the game page. I'm not saying there's anything wrong with 25 year old style games, but it puts a question mark in my mind.
Consider adding some flavor text or unusual graphics that hint at the game being based on that style, but with a modern take. Then the question mark becomes a hook. "Does that zombie have a smartphone or a magic book with icons?" Is a lot more interesting than "why is this game old looking?"
Number three, speaking of a modern take, consider showing the cards you will draw. Perhaps as an item or class if there isn't one already. If there is, consider making it far far more common. Ideally you could even allow players to stack a plan of moves and commit to them all at once for a bonus.
Right now there is a lot of cases where there's simply a right move to make. It isn't particularly fun knowing that a simple machine could be trained to do what I'm doing. By making things less random you allow players to plan moves in advance. The mechanical moves become filler that confuses finding perfect moves in the future. By lowering the randomness you can allow players to plan and strategize way more and way deeper.
Right now, it looks like luck and skill will be needed to win. Why does this game need luck?
I'm going to stop at four because I've had a long day, but lastly, I'm not sure exactly the tone you are going for, but the game could have a basic optional story and some basic art that depicts the hero as someone that lost his cognitive abilities due to combat and journal of fighting instructions. The cards are pages from his journal that help him remember how to fight. As he picks them up he learns better how to fight, but because they are ripped he keeps mixing them up. Each class can actually be the same guy with just different sets of pages that put on display a fraction of his power.
The story could have to do with not only collecting all the pages, but also organizing them in a helpful way when he has limited ability to think. You don't need to go all out, but a few basic comments about his unstable perspective of figuring out that he is the best fighter in the world could get players pumped about the idea of playing with cards and strategizing them.
Hope that helps.