you've got a pretty interesting concept here! lots of potential for expanding the rules and making new puzzles.
apart from little bugs like cards sometimes not updating when a neighboring card is placed, I feel its lacking a little clarity. for example, it took me a minute to notice that a card can give and take blood from any side, as the signs made it seen like the snake, for example, could only take blood from the bottom and left, and only give blood from the top and right.
maybe adding a little animation when a card gets and loses its full effect would work really well, too!
that said, very good work! I'd be interested to check it out again if you decided to continue work on it!