Super cool concept. I can tell there's probably a lot more you wanted to do with it (such as having more "meta" fields like the music) but this is a really good proof of concept, and I enjoyed the gameplay for a bit. It does suffer a little from the borders of the arena being invisible, leading to frustrating deaths, and the pause not kicking in early enough when the player wants to change cards.
My brain do be liking with when big number go brrr so you got me there.