Initially, I was very confused but after dying once to the jester, I got a much better understanding of the game.
Your use of the theme was very well done. At first, I just thought it cool but during the second boss fight,t I was able to strafe around enemies in a way that I could spam my cards a lot more than I otherwise could; this took the mechanic up a notch for me, in terms of fun.
Unfortunately, I wasn't able to beat the second boss. I figured the yellow cylinder was a shield and I tried attacking knights without their shields on but those knights would never die and the boss's shield would never disappear.
The art was well made. The animations for some of the attacks were very cool; the jester's jump is probably my favorite.
I wish there was more in the way of SFX. The weight of casting a spell or having to dodge a laser beam would be much more potent with SFX. Although, at least having music does greatly make up for what would otherwise be a silent game.
The whole card system between bosses is very cool and I like how you hide some of the cards early on. It gives the player something to look forward too while also avoiding overwhelming them.
A well-made game.