Brilliant, delightful game with a solid variety of monsters and items/ powerups, and that's easy to get into. Really glad I took the time to check it out. :)
Echoing what at least one other person said, I feel that this has a lot of potential if expanded upon and released as a paid version, especially if more cards are added overall, and also if more cards are collected to be shuffled into the deck as you play within a game, and that carry over from one game to the next. Toss some extra characters as well, and possibly even a smattering of story/ character development, and this one'd have all the makings of something truly special.
Even as it stands though, again, this is a real gem. Kudos! :D