The thing I don't like about Arsenic is it lacks any control besides controlling your enemy's health.
If you can control you enemy's health, you've basically won. Arsenic is an awesome weapon. Even when it gets exploded, it'll still remain in our hearts... and next to the opponents health bar. (unless they have purify)
I was still sticking around with boring rainbows when I made that post.
What I've found after experimenting with quite a few rushes is that Arsenic is an amazing card in pillarless rainbow rushes. For only 2 death quanta, you have something to fill your lonely weapon slot that screams "RUSH!" I rarely stack enough poison, though, before I either kill the opponent or Arsenic gets Exploded/Stolen, so Purify doesn't do too much. In Poison rushes, on the other hand...