After playing pvp some, I have to say this card would be insanely overpowered in some decks. There were plenty of situations where had my opponent been able to stop all my damage and just let his creatures/poison hit me for 2 turns, he would have won.
Imagine this in a death+physalia deck. lay on the damage, wait until you're almost dead, then just ride it out. It would be somewhat hard to chain these, since you'd need 5 water towers out, but with SoG or any sort of healing (miracles, for example), you could easily ride it out.
On that note, this would synergize beautifully with miracles. Some light dragons and toadfish for damage, these for end-game stalling, and miracles to help chain them. BAM.