I really like how the stats get kept between rounds, lets you charge up your cards ready for the boss fights, and the mechanic of attacking the right most first works very well since you have to think about which card you don't mind losing as much.
Potential improvements would mainly be a more detailed tutorial, took a while for me to realise the cooldown system. Maybe first explaining the mechanics without swapping (cooldowns ticking down each turn) would make it clearer, so the player understands the basic rules before adding complexity.
Also, some cards get quite OP, but since the bosses are also very powerful this isn't necessarily a problem.
Extra idea: could the enemy have an AI that also swaps tokens? That would add more depth so you can't just deny the enemies making moves by swapping away their 1s.