The size swapping mechanic is cool. It could allow for some really interesting puzzles. The random card mechanic is pretty interesting as well although I think you would need to introduce more enemy types, obstacles and hazards in order for it to work at its full potential.
I will say I accidentally glitched out of one of the rooms (the one with the spike traps moving up and down) by hitting the top of one and moving up into the ceiling. Then I couldn't get back in and I ended up falling infinitely. Obviously game jams don't give you much time to test everything properly, but if you continue to work on the game then you should have a look at fixing it.
Great effort ^-^