I have a suggestion. Make it utilize max hp.
This way it solves the problem that BBing it when your opponent is at 100 health won't heal them any and increase the damage done by 20 at the same time.
This also makes the card itself better, which I think is needed. Unstable Gas is one card that does 20 damage. This is something that needs at least two cards and does only 15 unless you buff it somehow with ANOTHER card (and one of those cards makes it rather OP). Granted, it only needs 1-2 quanta types to work, but the two card fact makes trumps that.
So to balance it by taking away the OP part (Basilisk Blood) and making the card better in a different way, I suggest making it alter your opponent's max hp rather than current hp. Maybe 15 hp is too powerful then; maybe it could be lowered to something like 12.