It definitely takes some time to understand the mechanics without a neat tutorial, but I think I got there in the end. Although I never learned how to sacrifice a card lol.
But I see the potential in this and I think it could be really fun deck builder with some fun mechanics. Right now it is lacking the tutorial type of thing which familiarize the player with the concept and mechanics plus some UI elements that makes it more clear on what phase of your turn you are in, where cards will attack, what cards you can actually summon and when, etc. The card designs are cool though and I wish the flavor text was there! I liked the sounds too it was simple but really gave that summoning feeling to the game. This is a great start and the blood-mechanic is over all simple but I think you could do a lot with it as the game progresses. Good work!