I don't understand the earth cost for the ability.
Might as well not have an ability though, since the toadfish is probably better in almost any situation, as it can kill. Water has quite a bit of CC for the amount of cards in the game, as well, so I can't imagine something like this being used too much, and less still since it can't kill, and earth/water doesn't have enough synergy otherwise to get this card being used.
I also am a bit unsure about the cumulative part, but I assumed that it means that one use will give you 2 damage on the target creature per turn, until the target is changed.
Anyway, I'm not sure how good this would be. How did you imagine it being used?