Here is the problem I see. With this card I would be playing

use water pendulums for purity. Jade Dragon or Bone Dragon, Hit Jade Dragon with Biotoxin purify, rinse repeat. If you could manage 2 or 3 bio toxins, you could play them all at once, the just purify the Dragon, your doing 30 poison damage, which most decks probably couldn't deal with. Maybe if you could limit how many times you could use this a turn that would be good. That or buff the cost. Just IMO and theory.