I never said he was invincible. I just said he could not die. That means his suffering can be much worse then someone who could. That was a great weakness in itself.

By invincible, I'm assuming you mean that he can not be hurt. So he is FAR from invincible, he just can not die. (Only suffer the pain of coming close to it) That would render him pretty helpless if someone stabs a sword through his gut. He would lay there for days, until he finally got the strength to pull it out.

He also is not going to turn into the beast every five seconds. I specifically said that the beast is a last resort. Even if he does transform, he is still not invincible, just stronger.

(Can you point out where I said he was invincible?)