Ok, i had about 20 hours of bus rides and lots of time to myself the past couple weeks. I've beaten the first three bosses (though i had to keep count of how much HP the boss had left for the second two bosses on a piece of paper). The third boss, Evolution, took me forever to kill. It seems like they've got a ton of high-damage attack cards. Also, Ambush is super annoying! Though really that's how i beat the third boss, as i used Mastermind to steal the boss' Ambush and then killed them with it

After that i haven't been able to beat any of the new bosses. Today on the bus i finally got to the 4th round (after making a comeback from 1HP vs. the other player's 15HP in the 3rd round!), but of course died.
Btw, one of my new favorite cards is Reminisce. I love using that with those cards that do major damage (eg. Fireball or Grim Claws) or with Contaminate after the enemy just used an antidote.
Also, i think there's a mistake in the description for Fireball. It says "Deals 5 damage to your opponent. Adds 1º" but really it adds 2 spheres. The icon shows that it adds 2 spheres.
Anyway, this game is great and super addicting. But i dunno if i'll ever be able to beat the other three bosses. I wish i could find some more antidotes, though. Being poisoned sucks. I dunno which set of cards to buy to get those, though.
EDIT: I forgot to mention that i am really impressed by the AI, it seems to know how/when to use the cards (at least as well as i do, heh) and doesn't just randomly play a card.