I do like this idea, but it does need some balancing. A cost is definitely a must imo. Even 1 | 2 will do. The problem is is that is basically is a pillar with an effect added on to it, and reusable, which is very powerful. Ultimately the issue is the free cost allows for use in any deck, and you can completely disregard gaining the pillar/tower. Also, unlike OT, I think the idea of poison being added onto yourself along with some direct damage, particularly such that any healing mechanics (especially those out of reach of destruction by the opponent) available may put this as a broken card.
I really want it to be free so that it won't be slaughtered by decks like Pestal or Black Hole spam and the like. I think I will raise the HP cost and submit it to the Crucible, but, if there is any other reason that the card shouldn't be free that would make it ridiculously overpowered in some type of deck, then please tell me.
Also, when I said that it poisoned you, I meant that it only poisons you; there is no direct damage. The upgraded version deals direct damage (so it can be used for longer). They were ridiculously broken in that I underestimated the power of being unable to deck out. Here's the cards from before:
For some reason, I put zeroes for the card cost.