I'm not going to say I think Immortal is a really good card, but it doesn't have to worry about Congeal(+Shockwave), Rewind, Basilisk's Blood, Antimatter, etc... or getting hit three times before he can do something.
With all the creative ways to get around needing your opponent to damage it, I could see decreasing the damage to 20 (20/40 unupped, 20/50 upped) though. Blue Nymph or Unstable Gas makes for a costly Duo+sacrificing your mark to make
. I think the real power of this guy lies in boosting mono gravity. I do like the idea of a duo with fire and Rage Elixirs (trio with PU if possible), I think mono gravity may like the Colossus more than anything else.